Add SQLite note and profile cache (roadmap #3)

- Rust: rusqlite (bundled) with WAL mode; wrystr.db in app data dir
  - db_save_notes: upsert batch of raw event JSON, prune to 500 kind-1 notes
  - db_load_feed: return N most-recent kind-1 raws for instant startup display
  - db_save_profile / db_load_profile: cache NDKUserProfile JSON by pubkey
  - Falls back to in-memory SQLite if the on-disk open fails
- src/lib/db.ts: typed invoke wrappers; all errors silenced (cache is best-effort)
- feed store: loadCachedFeed() populates notes before relay connects;
  loadFeed() merges fresh+cached (so relay returning fewer notes doesn't
  erase cached ones), then saves fresh notes to SQLite
- useProfile: reads SQLite cache to show avatar/name instantly while
  relay request is in-flight; saves result to SQLite after relay responds
- Feed: calls loadCachedFeed() first → notes visible before relay connects

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src-tauri/Cargo.lock

@@ -8,6 +8,18 @@ version = "2.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "320119579fcad9c21884f5c4861d16174d0e06250625266f50fe6898340abefa"
 
+[[package]]
+name = "ahash"
+version = "0.8.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a15f179cd60c4584b8a8c596927aadc462e27f2ca70c04e0071964a73ba7a75"
+dependencies = [
+ "cfg-if",
+ "once_cell",
+ "version_check",
+ "zerocopy",
+]
+
 [[package]]
 name = "aho-corasick"
 version = "1.1.4"
@@ -862,6 +874,18 @@ dependencies = [
  "pin-project-lite",
 ]
 
+[[package]]
+name = "fallible-iterator"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2acce4a10f12dc2fb14a218589d4f1f62ef011b2d0cc4b3cb1bba8e94da14649"
+
+[[package]]
+name = "fallible-streaming-iterator"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7360491ce676a36bf9bb3c56c1aa791658183a54d2744120f27285738d90465a"
+
 [[package]]
 name = "fastrand"
 version = "2.3.0"
@@ -1364,6 +1388,15 @@ version = "0.12.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8a9ee70c43aaf417c914396645a0fa852624801b24ebb7ae78fe8272889ac888"
 
+[[package]]
+name = "hashbrown"
+version = "0.14.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e5274423e17b7c9fc20b6e7e208532f9b19825d82dfd615708b70edd83df41f1"
+dependencies = [
+ "ahash",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.15.5"
@@ -1379,6 +1412,15 @@ version = "0.16.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "841d1cc9bed7f9236f321df977030373f4a4163ae1a7dbfe1a51a2c1a51d9100"
 
+[[package]]
+name = "hashlink"
+version = "0.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6ba4ff7128dee98c7dc9794b6a411377e1404dba1c97deb8d1a55297bd25d8af"
+dependencies = [
+ "hashbrown 0.14.5",
+]
+
 [[package]]
 name = "heck"
 version = "0.4.1"
@@ -1884,6 +1926,17 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "libsqlite3-sys"
+version = "0.30.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2e99fb7a497b1e3339bc746195567ed8d3e24945ecd636e3619d20b9de9e9149"
+dependencies = [
+ "cc",
+ "pkg-config",
+ "vcpkg",
+]
+
 [[package]]
 name = "linux-raw-sys"
 version = "0.12.1"
@@ -2844,6 +2897,20 @@ dependencies = [
  "web-sys",
 ]
 
+[[package]]
+name = "rusqlite"
+version = "0.32.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7753b721174eb8ff87a9a0e799e2d7bc3749323e773db92e0984debb00019d6e"
+dependencies = [
+ "bitflags 2.11.0",
+ "fallible-iterator",
+ "fallible-streaming-iterator",
+ "hashlink",
+ "libsqlite3-sys",
+ "smallvec",
+]
+
 [[package]]
 name = "rustc_version"
 version = "0.4.1"
@@ -4122,6 +4189,12 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "vcpkg"
+version = "0.2.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "accd4ea62f7bb7a82fe23066fb0957d48ef677f6eeb8215f372f52e48bb32426"
+
 [[package]]
 name = "version-compare"
 version = "0.2.1"
@@ -4996,6 +5069,7 @@ name = "wrystr"
 version = "0.1.1"
 dependencies = [
  "keyring",
+ "rusqlite",
  "serde",
  "serde_json",
  "tauri",