feat: add YouTube subtitles, local transcription, self-updating yt-dlp/Deno, X Article and thread titles (#39)

- Capture YouTube subtitles by default (opt-out in UI, API, CLI --no-subtitles)
- Summarize YouTube videos from subtitles; fetch on demand, then local transcription, then error
- Local transcription fallback: Whisper, Parakeet, Phonon-2 (English only)
- Runtime-resolved, self-updating yt-dlp and Deno JS runtime (fixes YouTube 403s)
- Settings > Instance > yt-dlp: status and in-app update without restart
- X Article titles from article.title, with idempotent startup backfill
- Thread title generation (single and bulk) with per-provider cheap models
- Per-provider title model settings in Settings > Instance
- Docs, mental model, AGENTS.md and transcription spec updated

Cargo.lock

@@ -97,9 +97,7 @@ dependencies = [
  "chrono",
  "clap",
  "regex",
- "reqwest",
  "rusqlite",
- "serde_json",
  "tempfile",
 ]
 
@@ -111,6 +109,7 @@ dependencies = [
  "base64",
  "chrono",
  "hex",
+ "libc",
  "regex",
  "reqwest",
  "rusqlite",
@@ -119,6 +118,7 @@ dependencies = [
  "sha3",
  "tempfile",
  "uuid",
+ "zip",
 ]
 
 [[package]]
@@ -431,6 +431,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "crc32fast"
+version = "1.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "01a7799fd6b852db0e61728dde9a204c423b44d689dbd432522543614b490e78"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "crypto-common"
 version = "0.1.6"
@@ -518,6 +527,15 @@ version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "52051878f80a721bb68ebfbc930e07b65ba72f2da88968ea5c06fd6ca3d3a127"
 
+[[package]]
+name = "flate2"
+version = "1.1.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e634e2e0ebac1ee034020da1ca582e17ffe4e0f5e985823721e168928136dcb"
+dependencies = [
+ "zlib-rs",
+]
+
 [[package]]
 name = "fnv"
 version = "1.0.7"
@@ -1933,6 +1951,12 @@ version = "0.2.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e421abadd41a4225275504ea4d6566923418b7f05506fbc9c0fe86ba7396114b"
 
+[[package]]
+name = "typed-path"
+version = "0.12.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e28f89b80c87b8fb0cf04ab448d5dd0dd0ade2f8891bae878de66a75a28600e"
+
 [[package]]
 name = "typenum"
 version = "1.19.0"
@@ -2469,6 +2493,25 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "zip"
+version = "8.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2d04a6b5381502aa6087c94c669499eb1602eb9c5e8198e534de571f7154809b"
+dependencies = [
+ "crc32fast",
+ "flate2",
+ "indexmap",
+ "memchr",
+ "typed-path",
+]
+
+[[package]]
+name = "zlib-rs"
+version = "0.6.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b268e58e7c693d7c271f93ffc4ba3b380412554231c85bf61ca7af91042a4112"
+
 [[package]]
 name = "zmij"
 version = "1.0.21"