refactor: extract node:sqlite-free parsing.mjs so the core can be app-consumable (Phase 5d-1)

Move all pure parse/discover helpers (message extraction, project-path, codex
helpers, discovery) out of db.mjs/indexer.mjs into scripts/parsing.mjs, which
imports only node:fs/path/os. Providers now import from parsing.mjs, so the
provider import graph no longer transitively loads node:sqlite — a prerequisite
for the app (Electron/Node without node:sqlite) to consume the compiled core.
Verbatim move, no behavior change; indexer.mjs 840→209 lines. 119/119.

scripts/providers/claude.ts

@@ -12,9 +12,8 @@ const fs = require('node:fs');
 
 import {
   extractText, extractContentType, extractMessageIsMeta,
-  filePath, trunc, truncJson, readLines,
-} from '../db.mjs';
-import { discoverJsonlFiles } from '../indexer.mjs';
+  filePath, trunc, truncJson, readLines, discoverJsonlFiles,
+} from '../parsing.mjs';
 
 import type { Cursor, DiscoverContext, IndexRecord, IndexUnit, Provider } from './types.ts';
 

scripts/providers/codex.ts

@@ -12,14 +12,14 @@ import { createRequire } from 'node:module';
 const require = createRequire(import.meta.url);
 const fs = require('node:fs');
 
-import { trunc, truncJson, readLines } from '../db.mjs';
 import {
+  trunc, truncJson, readLines,
   discoverCodexJsonlFiles, normalizeObservedCwd, projectSlugFromPath,
   codexRawId, codexDbId, codexCallId, codexLineUuid, codexParentThreadId,
   codexIsGuardianThread, codexAgentNickname, codexAgentRole, codexUsage,
   codexEventText, codexMessagePayloadText, codexVisibleMessageKey,
   codexToolInput, codexToolOutput,
-} from '../indexer.mjs';
+} from '../parsing.mjs';
 
 import type { Cursor, DiscoverContext, IndexRecord, IndexUnit, MessageRecord, Provider } from './types.ts';