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-api/src/main.rs

@@ -11,7 +11,7 @@ use chrono::{DateTime, Datelike, NaiveDate, Utc};
 use clap::Parser;
 use moments_core::{EventReader, reshape};
 use moments_data::PgStore;
-use moments_entities::{DailyCount, EventQuery, ProjectSummary, Source, SourceSummary, TimelineItem};
+use moments_entities::{DailyCount, EventQuery, LanguageDailyCount, ProjectSummary, RepoLanguage, Source, SourceSummary, TimelineItem};
 use serde::Deserialize;
 use tower_http::{cors::CorsLayer, trace::TraceLayer};
 use tracing::info;
@@ -57,6 +57,8 @@ async fn main() -> anyhow::Result<()> {
         .route("/v1/sources", get(list_sources))
         .route("/v1/projects", get(list_projects))
         .route("/v1/activity/daily", get(daily_counts))
+        .route("/v1/languages/daily", get(language_daily_counts))
+        .route("/v1/languages/repos", get(repo_languages))
         .route("/v1/forge/{source}/{*rest}", get(forge_proxy))
         .route("/v1/og/contributions.png", get(og_contributions))
         .with_state(state)
@@ -157,6 +159,23 @@ async fn daily_counts(
     Ok(Json(counts))
 }
 
+async fn language_daily_counts(
+    State(state): State<AppState>,
+    Query(params): Query<DailyCountsParams>,
+) -> Result<Json<Vec<LanguageDailyCount>>, ApiError> {
+    let to = params.to.unwrap_or_else(|| Utc::now().date_naive());
+    let from = params.from.unwrap_or_else(|| to - chrono::Duration::days(365));
+    let counts = state.store.language_daily_counts(from, to).await.map_err(internal)?;
+    Ok(Json(counts))
+}
+
+async fn repo_languages(
+    State(state): State<AppState>,
+) -> Result<Json<Vec<RepoLanguage>>, ApiError> {
+    let langs = state.store.repo_languages().await.map_err(internal)?;
+    Ok(Json(langs))
+}
+
 async fn og_contributions(
     State(state): State<AppState>,
 ) -> Result<impl IntoResponse, ApiError> {