feat: language stream graph on dashboard

Full-stack feature showing programming languages by commit activity
as a stream graph on the dashboard.

Backend:
- migration: repo_languages table (source, repo, language, bytes, color)
- worker: fetch language breakdowns via GitHub GraphQL (batched,
  20 repos/request) and Gitea REST API during poll cycles
- API: GET /v1/languages/daily (daily commit counts per language),
  GET /v1/languages/repos (all stored repo language data)
- fix timezone bug in daily_counts and language_daily_counts: the
  PostgreSQL server timezone (Europe/Sofia, UTC+3) shifted day
  boundaries, miscounting events near midnight. Now uses explicit
  UTC boundaries in generate_series JOINs.
- use per-source CASE for repo name extraction in language query
  to match gitea payload structure (repo.full_name vs repo.name)
- Gitea languages use GitHub colors via COALESCE fallback

Frontend:
- LanguageStreamGraph component: pure SVG stream graph, weekly
  buckets, centered baseline, top 8 languages + Other, GitHub
  canonical language colors, legend with color dots
- DashPage/ProjectPage: fetch repo languages once via new endpoint
  instead of per-repo forge proxy calls (eliminates 200+ GitHub
  API calls and 403 rate limit errors)
- removed fetchLanguages forge proxy wrapper (dead code)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/moments-data/src/github_repo.rs

@@ -20,7 +20,7 @@ use std::sync::Arc;
 use async_trait::async_trait;
 use chrono::{DateTime, Utc};
 use moments_core::{EventSource, EventWriter, PollerStateStore, SourceError};
-use moments_entities::{Event, Source};
+use moments_entities::{Event, RepoLanguage, Source};
 use reqwest::{Client, header};
 use serde_json::Value;
 use tracing::{debug, warn};
@@ -296,6 +296,105 @@ impl GithubRepoSource {
         self.state.save(&state_key, None, newest).await?;
         Ok(total)
     }
+
+    /// Batch-fetch language breakdowns for repos via GraphQL, upserting
+    /// into repo_languages. Repos are batched using GraphQL aliases to
+    /// minimise round trips.
+    async fn fetch_languages(&self, repos: &[Repo]) -> Result<usize, SourceError> {
+        let token = match &self.config.token {
+            Some(t) => t,
+            None => return Ok(0),
+        };
+
+        let mut total = 0usize;
+        for chunk in repos.chunks(20) {
+            let mut fragments = Vec::with_capacity(chunk.len());
+            for (i, repo) in chunk.iter().enumerate() {
+                let parts: Vec<&str> = repo.full_name.splitn(2, '/').collect();
+                if parts.len() != 2 {
+                    continue;
+                }
+                fragments.push(format!(
+                    r#"r{i}: repository(owner: "{}", name: "{}") {{ languages(first: 20, orderBy: {{field: SIZE, direction: DESC}}) {{ edges {{ size node {{ name color }} }} }} }}"#,
+                    parts[0], parts[1]
+                ));
+            }
+            if fragments.is_empty() {
+                continue;
+            }
+
+            let query = format!("{{ {} }}", fragments.join(" "));
+            let body = serde_json::json!({ "query": query });
+
+            let resp = self
+                .client
+                .post("https://api.github.com/graphql")
+                .header(header::AUTHORIZATION, format!("Bearer {token}"))
+                .header(header::USER_AGENT, USER_AGENT)
+                .header(header::CONTENT_TYPE, "application/json")
+                .json(&body)
+                .send()
+                .await
+                .map_err(|e| SourceError::Http(e.to_string()))?;
+
+            if !resp.status().is_success() {
+                warn!(status = %resp.status(), "GraphQL language fetch failed");
+                break;
+            }
+
+            let data: Value = resp
+                .json()
+                .await
+                .map_err(|e| SourceError::Parse(e.to_string()))?;
+
+            if let Some(errors) = data.get("errors").and_then(Value::as_array) {
+                if let Some(msg) = errors.first().and_then(|e| e.get("message")).and_then(Value::as_str) {
+                    warn!(error = %msg, "GraphQL language fetch had errors");
+                }
+            }
+
+            let data_obj = match data.get("data") {
+                Some(d) => d,
+                None => continue,
+            };
+
+            let mut languages = Vec::new();
+            for (i, repo) in chunk.iter().enumerate() {
+                let alias = format!("r{i}");
+                let edges = data_obj
+                    .get(&alias)
+                    .and_then(|r| r.get("languages"))
+                    .and_then(|l| l.get("edges"))
+                    .and_then(Value::as_array);
+                if let Some(edges) = edges {
+                    for edge in edges {
+                        let size = edge.get("size").and_then(Value::as_i64).unwrap_or(0);
+                        let name = edge
+                            .get("node")
+                            .and_then(|n| n.get("name"))
+                            .and_then(Value::as_str);
+                        let color = edge
+                            .get("node")
+                            .and_then(|n| n.get("color"))
+                            .and_then(Value::as_str);
+                        if let Some(name) = name {
+                            languages.push(RepoLanguage {
+                                source: Source::Github,
+                                repo: repo.full_name.clone(),
+                                language: name.to_string(),
+                                bytes: size,
+                                color: color.map(String::from),
+                            });
+                        }
+                    }
+                }
+            }
+            total += self.writer.upsert_repo_languages(&languages).await?;
+        }
+
+        debug!(total, "repo languages updated");
+        Ok(total)
+    }
 }
 
 #[async_trait]
@@ -327,6 +426,10 @@ impl EventSource for GithubRepoSource {
             }
         }
 
+        if let Err(e) = self.fetch_languages(&repos).await {
+            warn!(error = %e, "language fetch failed; continuing");
+        }
+
         self.state.touch(SOURCE_NAME).await?;
         debug!(ingested = total, repos = repos.len(), "github-repo poll complete");
         Ok(total)