refactor: migrate templates/ → registry/examples/ (#253)

## What

PR 2/17 of the catalog system rollout. **Physical directory rename.** Stacks on #252.

- `git mv templates/ registry/examples/` — all 8 example directories (`decision-tree`, `kinetic-type`, `nyt-graph`, `play-mode`, `product-promo`, `swiss-grid`, `vignelli`, `warm-grain`) plus `templates.json`
- `packages/cli/src/templates/remote.ts` — `TEMPLATES_DIR` constant from `"templates"` → `"registry/examples"`, exported for regression testing
- `scripts/generate-template-previews.ts` — `remoteTemplatesDir` resolved to the new path
- Comment updates in `packages/cli/src/templates/generators.ts` and `packages/cli/src/commands/init.ts`
- New regression test `packages/cli/src/templates/remote.test.ts` pinning the path constants so future reverts fail a test instead of silently breaking installed CLIs

Design doc: [Hyperframes Catalog System](https://www.notion.so/heygen/Hyperframes-Catalog-System-Design-Plan-341449792c69813f899dcd53b4c0383a).

## Why

The current `templates/` directory is a flat "things that scaffold projects" bucket. The catalog model splits content into three tiers: **examples** (full projects — what today's templates are), **blocks** (sub-compositions), and **components** (effect snippets). `registry/examples/` is the canonical home for what was previously at `templates/`, and this PR makes room for `registry/blocks/` and `registry/components/` in future PRs without top-level clutter.

## How

- `git mv` preserves file history — GitHub renders these as renames, not deletions + additions.
- Remote template fetch via giget reads `TEMPLATES_DIR`, so updating that one constant is sufficient for the CLI's remote code path.
- The CLI's **internal** `packages/cli/src/templates/` directory (which holds the `blank` and `_shared` bundled assets plus `generators.ts`/`remote.ts`) is a separate concept and is **not** touched here. Renaming that module belongs to PR 3 where the abstraction changes to a registry resolver.
- `templates.json` keeps its existing shape and location (now at `registry/examples/templates.json`). **PR 3 will transform it** to the new `registry.json` shape introduced in PR 1 and generate a per-item `registry-item.json` for each example. Leaving the shape change to PR 3 keeps this PR a pure physical move.

## ⚠️ Breaking change for previously-installed CLIs (`hyperframes@0.1.0` – `0.3.0`)

**What happens:** every published CLI version has `TEMPLATES_DIR = "templates"` baked in. After this PR lands on `main`, those CLIs will 404 on:

- `raw.githubusercontent.com/heygen-com/hyperframes/main/templates/templates.json` (manifest list) — caught silently in `listRemoteTemplates`, so the template picker falls back to showing only `blank`
- `github:heygen-com/hyperframes/templates/<id>#main` (giget download) — raises "Template downloaded but missing index.html"

**Decision: accept the break.** Hyperframes is pre-1.0 OSS with a small installed base; complex mitigations (dual-path fetch, redirect stubs, manifest-at-old-path with empty array) add permanent maintenance cost for a one-time rename.

**Rollout plan:**

1. Merge #252 (PR 1 — types & schemas) first
2. Merge this PR (#253)
3. Ship a patched CLI release (`hyperframes@0.3.1`) in the same work-day. Already-pinned old CLIs break on remote examples, but upgrading restores full functionality
4. Note the break in release notes + `CHANGELOG.md` under the `0.3.1` entry

Users still on an older CLI will see the failure only if they invoke `hyperframes init` with `--template <non-blank>`; `--template blank` (bundled) continues to work offline on every version.

## Test plan

- [x] `bun run test` in `packages/cli`: **57 passed** (was 55 on main, +2 regression tests for the path constants). Same 4 pre-existing failures (SRT/VTT whisper normalizer + `lintProject` clean-project test) — unchanged from main. No regressions
- [x] **Manual smoke test**: `hyperframes init /tmp/x --template blank` works (bundled code path, unchanged)
- [x] `bunx oxfmt --check` + `bunx oxlint`: clean
- [x] `bun run typecheck` (core + studio, pre-commit hook): clean
- [ ] **Manual smoke test for remote fetch (`--template warm-grain`)** — not verifiable locally before merge. Remote fetch resolves `github:heygen-com/hyperframes/registry/examples/<id>#main`, which doesn't exist until this PR lands. Will work on `main` immediately after merge.

## Breaking / migration

- Internal repo path changes only. `--template` CLI flag continues to accept the same template names.
- See "Breaking change for previously-installed CLIs" above — decision is to ship a simultaneous CLI release rather than add a compat shim.

## Commits

1. `d691bd1` — initial rename + CLI path constant update
2. `fc0c642` — review feedback: docstring fix, regression tests, clarifying comment in `init.ts`, export constants for testing

## Stacks on

#252 — base branch. When #252 merges, this rebases onto `main`.

## Next in stack

PR 3 — `feat(cli): registry resolver + installer`. Transforms `templates.json` to the new `registry.json` shape (from PR 1's schema), generates `registry-item.json` for every existing example, introduces `packages/cli/src/registry/{resolver,installer,remote}.ts`, renames the `packages/cli/src/templates/` CLI module, and refactors `init` to call through the new abstraction.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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