Follow-ups for .func/config.json (PR #5010)

Follow-ups deferred from PR #5010 (`.func/config.json` bare-minimum scaffold). Tracking here so we don't lose them.

### Deferred items

- [ ] **Mismatch warning** when `.func/config.json` disagrees with resolver auto-detection (today we trust config silently).
- [ ] **`InitCommand` reads config** to seed selection (today init writes config but doesn't read it).
- [ ] **`$schema` URL + JSON schema file** published for editor IntelliSense.
- [ ] **`.gitignore` template** updates so transient `.func/` artifacts (state, logs, azurite data) are ignored while `.func/config.json` is committed.
- [ ] **README / `docs/` updates** documenting the file, schema, and precedence chain.
- [ ] **Standalone E2E test** covering the full precedence chain (`--stack` > `.func/config.json` > host.json gate > `FUNCTIONS_WORKER_RUNTIME` > resolver claims).
- [ ] **Per-workload extension area** in the schema, **walk-up discovery** from cwd, and **mirroring to `main` / `in-proc` branches**.

PR: #5010

Review the deferred-items checklist for .func/config.json, InitCommand, host.json, FUNCTIONS_WORKER_RUNTIME, README/docs, and the standalone E2E test. Start by determining which item can be scoped independently; done means its corresponding schema, precedence behavior, ignore rules, documentation, or test is implemented and verified.

Written by the indexing model from the issue text.