v1.108.90 — get_endpoint_impact (endpoint-centric blast radius)

Added

• get_endpoint_impact — endpoint-centric impact analysis: "what breaks if I change this HTTP endpoint?" Give it an endpoint (GET /users or /users, verb optional) or a handler_symbol_id and it resolves the route to its handler, then fuses the existing impact primitives into one read-only answer — importing files + callers (blast radius) and the templates the handler renders.
• Unified endpoint resolution over coverage the index already exposes: string-dispatch routes via flow_edges (Django/Express/Flask/Rails) and decorator routes via the gateway classification get_signal_chains uses (Flask/FastAPI/Spring), matched by verb + path (exact, then suffix).

Standard tier (alongside get_blast_radius / get_pr_risk_profile), so core_compact is unaffected. New tools/get_endpoint_impact.py; tests/test_endpoint_impact.py (10). Full suite 4882 passed. No INDEX_VERSION bump.

First slice of the framework-routes work. Deeper path resolution — FastAPI APIRouter(prefix=) / include_router composition and Spring class-level @RequestMapping inheritance — is the follow-on that enriches this same endpoint table; until then those routes match by local path or via handler_symbol_id.