chore: clarify/resolve ts-node vs dist worker mismatch (stale dist hazard)

## Problem
Currently, `npm run index` runs the main CLI via `ts-node`, but full + incremental indexing spawn worker threads from `dist/utils/producer_worker.js`.

This creates two user-facing issues:

1) **README / Quick Start ambiguity**
- A user can reasonably expect `npm install` + `npm run index ...` to work.
- In practice, indexing fails unless `dist/` exists (i.e., you must run `npm run build` first), because worker threads are hard-coded to load from `dist/`.

2) **Stale artifact / mixed-version hazard**
- If `dist/` exists but is stale, a single run can execute **new code** in the main process (ts-node) while executing **old code** in the worker (dist JS).
- This is subtle and hard to diagnose.

Evidence in code (paths are repo-relative):
- `src/commands/full_index_producer.ts` and `src/commands/incremental_index_command.ts` build worker path via:
- `path.join(process.cwd(), 'dist', 'utils', 'producer_worker.js')`

## Why this matters
- Consumers want deterministic behavior: one run should not mix sources of truth.
- Docs shouldn’t imply `npm run build` is optional if runtime depends on `dist/`.

## Proposed direction: explicit execution modes (avoid auto-detect)
Recommend enforcing a strict invariant: **within one run, main + workers come from the same source**.

### Option 1 (consumer-first / production default): dist-only
- Make the default consumer entrypoint run compiled output end-to-end.
- Change scripts so `npm run index` runs `node dist/index.js index ...` (or a wrapper that requires `npm run build`).
- Workers continue to load from `dist/`.
- Add a separate dev command for contributors.

### Option 2 (dev convenience): explicit dev/source mode
- Add `npm run index:dev` (or similar) that runs main via `ts-node` AND runs workers via TS as well.
- Crucially: dev mode should **never** load from `dist/` (even if it exists), to avoid the stale artifact hazard.

## Suggested script split
- `npm run build` -> `tsc`
- `npm run index` -> `node dist/index.js index` (requires build)
- `npm run index:dev` -> `ts-node src/index.ts index` (and worker threads also use TS)

## Doc follow-up
- Update README Quick Start to reflect the chosen default (likely dist-only), and optionally mention the dev command for contributors.

## Acceptance criteria
- Running the tool from source does not accidentally consume stale `dist/`.
- Running the tool in production (Docker/systemd/cron) uses compiled JS consistently.
- README Quick Start matches actual runtime requirements.

Read src/commands/full_index_producer.ts and src/commands/incremental_index_command.ts to trace how worker paths are selected, then inspect the npm scripts and README Quick Start. Compare the proposed source and compiled execution modes against the acceptance criteria. Done means main and worker code use one consistent source per run and the Quick Start documents the required command sequence.

Written by the indexing model from the issue text.