feat(auth): JWT-or-static middleware + /.well-known/oauth-protected-resource (issue #5)

- internal/auth/jwt.go: JWTValidator via lestrrat-go/jwx/v2, JWKS auto-refresh
- internal/auth/bearer.go: replace Gitea PAT validation with JWT->static->default chain
- internal/gitea/client.go: always use service PAT; remove TokenFromContext lookup
- internal/config/config.go: add DexIssuerURL, MCPAudience, MCPResourceURL, StaticToken
- cmd/gitea-mcp/main.go: wire validator, fix /.well-known to return real AS list
- bearer_test.go: rewrite for new API

.skills/htmx-patterns/SKILL.md

@@ -0,0 +1,31 @@
+---
+name: htmx-patterns
+description: HTMX conventions — default attributes, form patterns, validation errors, hypermedia-first API design. Use when writing HTMX templates or Go handlers that return HTML fragments.
+---
+
+# HTMX patterns
+
+## Default attributes
+Always include on interactive elements:
+- `hx-indicator` for loading states
+- `hx-swap="innerHTML"` as default (explicit over implicit)
+- `hx-target` pointing to a specific ID, never `this` in production
+
+## Form pattern
+```html
+<form hx-post="/items" hx-target="#item-list" hx-swap="beforeend" hx-indicator="#spinner">
+  <input type="text" name="title" required>
+  <button type="submit">Add</button>
+  <span id="spinner" class="htmx-indicator">...</span>
+</form>
+```
+
+## Server-sent validation errors
+Return 422 with the error fragment, swap into the form's error container:
+```html
+hx-target-422="#form-errors"
+```
+
+## Prefer hypermedia over JSON
+If the endpoint returns data for display, return an HTML fragment.
+Only use JSON for machine-to-machine APIs or when a non-browser client needs it.