feat: JSON multi-profile runtime config for Gitea MCP (roadmap #10)

Let one MCP server select among named Gitea runtime profiles from a JSON file
instead of editing code or juggling many .env files:

    GITEA_MCP_CONFIG=/path/to/gitea-mcp.json
    GITEA_MCP_PROFILE=dev

- New gitea_config.py: load/validate the JSON, select the named profile, and
  resolve its token by env-var reference. Profiles supply base_url,
  profile_name, token_env, owner/repo, allowed/forbidden operations, and audit
  label.
- gitea_auth.get_profile() now overlays env over the selected JSON profile:
  explicit env vars win, the JSON profile fills only what env leaves unset.
- gitea_auth.get_auth_header() gains a JSON token_env fallback after explicit
  env tokens (env still wins).

Security / safety:
- Tokens are referenced by env-var NAME (token_env); an inline "token" is
  rejected and never echoed. The value is never stored in or returned as
  profile metadata.
- Fail-safe errors: missing file / invalid JSON / unknown or unset selected
  profile raise a clear ConfigError that never prints file contents or tokens
  (JSONDecodeError context is suppressed so the raw file text can't surface).
- No network calls during config parsing.
- Real config files are gitignored (gitea-mcp*.json), example kept.

Backwards compatible: with GITEA_MCP_CONFIG unset, behaviour is exactly the
prior env-only behaviour (all existing get_profile/get_auth_header tests pass
unchanged).

Docs: README JSON-profiles section + env table rows, .env.example placeholders,
gitea-mcp.example.json.
Tests: tests/test_config.py (22 cases) — env-only, selection, multiple
profiles, env-override precedence, missing file, invalid JSON, missing/unset
profile, inline-token rejection + redaction, and no-network-during-parse.

Refs #10. Note: issue #19 (env-based profiles) was already implemented and
closed; this JSON-file capability is adjacent new scope tracked under the
roadmap rather than reopening #19.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

gitea_auth.py

@@ -17,6 +17,8 @@ import urllib.error
 from email.utils import parsedate_to_datetime
 from dotenv import dotenv_values, load_dotenv
 
+import gitea_config
+
 # Load standard .env if present
 load_dotenv()
 
@@ -119,10 +121,20 @@ def get_auth_header(host):
         if not token:
             token = os.environ.get("GITEA_TOKEN")
 
+    # 3. Fall back to a JSON runtime-profile token reference (token_env).
+    #    Explicit env tokens above take precedence. A broken config never breaks
+    #    auth here — it fails closed to "no token"; the clear error surfaces via
+    #    get_profile() / startup instead.
+    if not token:
+        try:
+            token = gitea_config.resolve_token(gitea_config.resolve_profile())
+        except gitea_config.ConfigError:
+            token = None
+
     if token:
         return f"token {token}"
 
-    # 3. Try User/Password Basic auth
+    # 4. Try User/Password Basic auth
     user, password = get_credentials(host)
     if user and password:
         token_b64 = base64.b64encode(f"{user}:{password}".encode()).decode()
@@ -299,20 +311,49 @@ def get_profile():
     token continues to be resolved separately by ``get_auth_header`` and is
     never part of this metadata. Callers may surface the result safely.
 
+    A JSON runtime-profile config (``GITEA_MCP_CONFIG`` + ``GITEA_MCP_PROFILE``,
+    see ``gitea_config``) may supply these same fields as a base layer. Explicit
+    environment variables always override the JSON profile; the JSON profile
+    only fills fields the environment leaves unset. With no config configured,
+    behaviour is exactly the environment-only behaviour above.
+
     Returns:
         dict with 'profile_name', 'allowed_operations' (list),
         'forbidden_operations' (list), 'audit_label', 'token_source_name',
         and 'base_url'.
     """
-    name = (os.environ.get("GITEA_PROFILE_NAME") or "gitea-default").strip()
-    raw_ops = os.environ.get("GITEA_ALLOWED_OPERATIONS") or ""
-    ops = [o.strip() for o in raw_ops.split(",") if o.strip()]
-    raw_forbidden = os.environ.get("GITEA_FORBIDDEN_OPERATIONS") or ""
-    forbidden = [o.strip() for o in raw_forbidden.split(",") if o.strip()]
-    audit_label = (os.environ.get("GITEA_AUDIT_LABEL") or "").strip() or None
-    # A *name* of the token source (e.g. "GITEA_TOKEN"), never the token value.
-    token_source = (os.environ.get("GITEA_TOKEN_SOURCE") or "").strip() or None
-    base_url = os.environ.get("GITEA_BASE_URL") or None
+    # JSON layer (base). None when GITEA_MCP_CONFIG is unset; raises ConfigError
+    # on a misconfigured file/profile so the problem surfaces clearly at startup.
+    jp = gitea_config.resolve_profile() or {}
+
+    def _env_csv(env_key):
+        raw = os.environ.get(env_key)
+        if raw is None:
+            return None
+        return [o.strip() for o in raw.split(",") if o.strip()]
+
+    def _json_list(key):
+        val = jp.get(key)
+        return list(val) if isinstance(val, (list, tuple)) else []
+
+    # profile_name: env > JSON > default.
+    name = (os.environ.get("GITEA_PROFILE_NAME")
+            or jp.get("profile_name") or "gitea-default")
+    name = str(name).strip() or "gitea-default"
+
+    ops = _env_csv("GITEA_ALLOWED_OPERATIONS")
+    if ops is None:
+        ops = _json_list("allowed_operations")
+    forbidden = _env_csv("GITEA_FORBIDDEN_OPERATIONS")
+    if forbidden is None:
+        forbidden = _json_list("forbidden_operations")
+
+    audit_label = (os.environ.get("GITEA_AUDIT_LABEL") or "").strip() \
+        or (jp.get("audit_label") or None)
+    # A *name* of the token source (env var name / JSON token_env), never a value.
+    token_source = (os.environ.get("GITEA_TOKEN_SOURCE") or "").strip() \
+        or (jp.get("token_env") or None)
+    base_url = os.environ.get("GITEA_BASE_URL") or jp.get("base_url") or None
     return {
         "profile_name": name,
         "allowed_operations": ops,