fix(sse): import localDb through its real .ts extension (#10674)

[diegosouzapw]

Closes #10674.

Root cause

open-sse/services/combo.ts:90 imported "../../src/lib/localDb.js" — a .js suffix on a
module that only ever existed as .ts. Turbopack resolved it by accident; the dependency-tree
change in #10647 stopped doing so, and the instrumentation hook then died at boot with
MODULE_NOT_FOUND.

Every sibling import in that same file already uses .ts, so this was a one-off slip, not a
convention.

Impact this was causing

• npm run dev on the tip could not boot at all (the symptom base-red: dev server cannot boot on release/v3.8.50 tip — instrumentation fails with "Cannot find module '../../src/lib/localDb.js'" after #10647's lockfile change #10674 reports).
• Build App has been red for 60 consecutive runs on release/v3.8.50 — every run
  available through the API, none green. The failure cascades: once combo.ts fails to
  resolve, Next reports 29 Module not found errors, including Node builtins
  (child_process, dns, fs, tls, net, module) pulled into the Middleware/Instrumentation
  graphs. All 29 come from this single unresolved import.
• Deploy to VPS has been skipping as a consequence.

Validation

Before/after on the tip (df90591415), fresh npm ci, .build/next/dev cache cleared:

	result
before	Fatal: instrumentation hook failed during boot: Cannot find module '../../src/lib/localDb.js'
after	boots fully — migrations, schedulers, proxy-health all start; 0 Module not found

typecheck:core clean, eslint clean on all three files.

Second offender found by the guard

src/lib/usage/usageLedger.ts:1 had the same .js-on-a-.ts pattern. It never broke because
it is an import type, erased before resolution — a latent copy of the same bug, fixed here.

Guard

tests/unit/no-js-extension-on-repo-imports-10674.test.ts rejects relative .js specifiers
across open-sse/ and src/. Package specifiers stay allowed on purpose: publishing ESM under
.js is correct for real packages (@modelcontextprotocol/sdk/client/index.js and 25 others
in-tree). Proven to discriminate — re-introducing the .js suffix makes it fail, naming the
exact file and line.

[diegosouzapw]

Merging with the inherited base-red documented. None of the 10 red checks come from this PR (diff = 2 import specifiers + 1 new guard test):

• Docs Gates — stale counts across README/AGENTS/llm.txt/4 SVGs (153→154 migrations, 340→341 providers) after other merges landed.
• Fast Quality Gates — open-sse/executors/index.ts TS2345, geminiWeb.ts size, and 4 stryker tap.testFiles entries missing for sse-auth-exclusive-leases, aihorde-optional-api-key and responses-passthrough-openai-compatible — all other people's tests, reproduced locally on this branch.
• Unit Tests fast-path — Antigravity cloudcode envelope tests.
• Fast Production Build — the very defect this PR partially fixes; it needs fix(config): keep the SQLite driver out of the client bundle (#10692) #10695 on top to go green (see that PR's build evidence).

Tracked under #9985.