agent: lumotia-rebrand — fix QC blockers for phase 2

Phase 2 QC found three explicit blockers + a broader sweep needed:

Explicit (QC-named):
- crates/mcp/src/lib.rs:15 — SERVER_NAME public MCP wire identity
- crates/transcription/build.rs:59 — panic message prefix
- crates/llm/tests/content_tags_smoke.rs:7 — docstring -p flag

Swept (string literals + dev env vars + doc comments + test fixtures):
- crates/mcp/src/main.rs — eprintln log prefixes
- src-tauri/src/commands/diagnostics.rs — diagnostic filename + MAGNOTIA_VERSION
- src-tauri/src/commands/audio.rs — recording filename pattern lumotia-<secs>-...wav
- src-tauri/src/commands/fs.rs — test placeholder path
- crates/transcription/src/model_manager.rs — .lumotia-verified marker
- crates/storage/src/database.rs — lumotia-storage-ro-<pid> temp dirs + doc comments
- crates/cloud-providers/src/keystore.rs — LUMOTIA_API_KEY_<PROVIDER> env var
- crates/audio/src/{wav,decode}.rs — lumotia_test_* / lumotia_decode_* test fixtures
- crates/core/src/tuning.rs — LUMOTIA_INFERENCE_THREADS env var
- All MAGNOTIA_LLM_TEST_MODEL / MAGNOTIA_WHISPER_TEST_* env vars
- Doc comments referencing crate names

Excluded (intentional Phase 4/5 scope):
- magnotia_preferences, magnotia_history, magnotia_morning_triage_last_shown
  DB setting keys (Phase 5 paths.rs migration)
- magnotia_startup tracing target (Phase 4)
- crates/core/src/paths.rs (Phase 5 wholesale rewrite + migration shim)

cargo build --workspace passes. cargo test --workspace: 330 pass, 0 fail.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/cloud-providers/src/keystore.rs

@@ -7,7 +7,7 @@ use std::sync::{Mutex, OnceLock};
 /// exit. This avoids the undefined behaviour of mutating process environment
 /// variables from arbitrary threads while keeping the public API safe.
 ///
-/// `retrieve_api_key` still falls back to `MAGNOTIA_API_KEY_<PROVIDER>` environment
+/// `retrieve_api_key` still falls back to `LUMOTIA_API_KEY_<PROVIDER>` environment
 /// variables so externally injected secrets continue to work.
 ///
 /// TODO: Replace with the `keyring` crate (or platform-native credential
@@ -22,7 +22,7 @@ pub fn store_api_key(provider: &str, key: &str) {
 /// Retrieve an API key from Magnotia's process-local keystore.
 ///
 /// Returns a previously stored in-memory key when present, otherwise falls
-/// back to the read-only `MAGNOTIA_API_KEY_<PROVIDER>` environment variable so
+/// back to the read-only `LUMOTIA_API_KEY_<PROVIDER>` environment variable so
 /// operator-supplied secrets still work.
 pub fn retrieve_api_key(provider: &str) -> Option<String> {
     let env_key = provider_env_key(provider);
@@ -40,7 +40,7 @@ fn api_key_store() -> &'static Mutex<HashMap<String, String>> {
 }
 
 fn provider_env_key(provider: &str) -> String {
-    format!("MAGNOTIA_API_KEY_{}", provider.to_uppercase())
+    format!("LUMOTIA_API_KEY_{}", provider.to_uppercase())
 }
 
 #[cfg(test)]