fix(pipeline): stop creating Route nodes from URLs in config files

[mvanhorn]

What does this PR do?

Indexing a repo of only config files produced spurious Route nodes from arbitrary URL-like strings. The infra-route extractor (cbm_pipeline_extract_infra_routes in src/pipeline/pipeline.c) harvested any CBM_STRREF_URL string literal from any .yaml/.yml/.tf/.hcl/.toml file, regardless of whether the host file actually defines service routes.

This restricts the loose URL string-ref harvesting to genuine Infrastructure-as-Code files (Terraform / HCL) and additionally requires the value to be a bare URL:

• cbm_is_infra_route_source_file() — only .tf, .tf.json, .hcl are route sources. Generic config (config.yaml), dependency manifests (dependabot.yaml), container orchestration (compose.yaml), and Kubernetes / Kustomize manifests are excluded.
• cbm_is_bare_endpoint_url() — rejects command strings that merely embed a URL (e.g. a curl ... || exit 1 healthcheck), while still accepting query-string URLs.

Structured topic→endpoint bindings still flow through cbm_pipeline_process_infra_bindings(), so real infrastructure endpoints (Cloud Scheduler / Pub/Sub targets) continue to produce Route nodes.

Why this matters: per #521, a three-file repro (dependabot.yaml + config.yaml + compose.yaml) yielded four bogus routes — a Terraform registry URL, a JWKS discovery URL, an upstream service host, and a healthcheck shell command. None is a route the service serves; they inflate the Route set that get_architecture and cross-repo route matching depend on, making downstream matching noisier.

Checklist

• Every commit is signed off (git commit -s) — required, CI rejects
  unsigned commits (DCO, see CONTRIBUTING.md)
• Tests pass locally (make -f Makefile.cbm test)
• Lint passes (make -f Makefile.cbm lint-ci)
• New behavior is covered by a test (reproduce-first for bug fixes)

Testing notes

• Built the indexer and reproduced the issue: before the fix the three-file config repro produced the four Route nodes from Route nodes created from URL strings in config / non-source files #521; after the fix it produces zero. A Terraform .tf endpoint URL still produces an infra Route.
• Added unit tests in tests/test_pipeline.c:
  • infra_route_source_file_gate — Terraform/HCL accepted; dependabot/config/compose/k8s/kustomize/toml and .tfvars rejected.
  • infra_bare_endpoint_url_gate — bare URLs accepted; healthcheck/command strings rejected.

Fixes #521