refactor: drop engine pieces now owned by TechEngine (TechAPI = data + site)

TechAPI is now purely the curated dataset + public site + a lightweight bundled validator. The API server, ingestion crawlers, static-dump generator, coverage checks, full validation and the Pages build/deploy all live in TechEngine (linked as a submodule), so this removes the duplicated pieces to keep the two repos non-overlapping:

- remove app/ backend (config, database, main, models, routers, schemas, services), tests/, scripts/ (dump.py, seed.py), docs/ (API design), Dockerfile, docker-compose.yml, .env.example, .dockerignore, pyproject.toml
- remove .github/workflows/{deploy-pages,refresh-data,test}.yml (TechEngine owns build/deploy, dump refresh and tests)
- keep data/, site/, the lightweight validator (scripts/validate.py -> app/validate.py) and validate-data.yml, which self-checks then chains to TechEngine's full validation

Refs #1

Author: Seungpyo1007

.dockerignore

@@ -1,21 +1,16 @@
-<!-- PR title must follow Conventional Commits (§14.5), e.g. feat(api): add /compare endpoint -->
+<!-- PR title must follow Conventional Commits, e.g. feat(data/cpu): add EPYC Rome SKUs -->
 
 ## What & why
 
 <!-- What does this change and why? Link issues with "Closes #123". -->
 
-## How
+## Source
 
-<!-- Key implementation notes. -->
-
-## Testing
-
-<!-- How was this verified? Paste test output or screenshots. -->
+<!-- Cite the upstream source (vendor product page, Wikipedia infobox, datasheet). -->
 
 ## Checklist
 
-- [ ] Type hints on all new functions (§0.5.4)
-- [ ] Tests added/updated (§15)
-- [ ] `ruff check` and `pytest` pass locally
-- [ ] Data changes pass `python -m scripts.validate`
-- [ ] SPEC/README updated if behavior changed (§0.5.4)
+- [ ] `python -m app.validate` passes locally
+- [ ] Files live at the correct `data/<category>/<...>/<slug>.json` path
+- [ ] Slugs are kebab-case and unique within the category
+- [ ] `source_urls` cites at least one canonical reference

.env.example

@@ -1,17 +1,31 @@
 name: validate-data
 
+# Self-check: every PR runs the bundled lightweight validator. Heavy checks
+# (coverage gaps, schema migrations, ingestion smoke tests) live in TechEngine.
 on:
   pull_request:
     paths:
       - "data/**"
+      - "app/validate.py"
+  push:
+    branches: [main]
+    paths:
+      - "data/**"
+      - "app/validate.py"
 
 jobs:
-  validate:
+  self-validate:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
         with:
           python-version: "3.12"
-      - name: Validate seed JSON (§9.3, §15.3)
-        run: python -m scripts.validate
+      - name: Self-check (bundled validator)
+        run: python -m app.validate
+
+  engine-validate:
+    needs: self-validate
+    uses: GetTechAPI/TechEngine/.github/workflows/validate-data.yml@main
+    with:
+      data-ref: ${{ github.event.pull_request.head.sha || github.sha }}