refactor: convert f-string logging to lazy %-style format (G004)

Sweep all 1676 G004 violations across 112 files, converting
`logger.<level>(f"…{x}…")` to `logger.<level>("…%s…", x)`.

Why: ruff rule G004 was added to pyproject.toml to enforce lazy
%-style logging — defers formatting until the log level is enabled
and lets structured log tooling match the unformatted template.

Conversion preserves rendered output byte-for-byte:
- `{x}` → `%s` + `x`
- `{x!r}` / `{x!s}` / `{x!a}` → `%r` / `%s` / `%a`
- Format specs (`{x:.2f}`, `{x:>10}`) → `%s` + `format(x, 'spec')`
  (printf-style specs aren't 1:1 with Python format specs, so we
  delegate to `format()` to keep identical output)
- Literal `%` → `%%`
- Concatenated f-strings (`f"a {x} " "b"`) flattened
- Trailing kwargs (`exc_info=True`) preserved

Verified:
- `uv run ruff check --select G004` → 0 violations
- `uv run ty check -- nextcloud_mcp_server` → passes
- `uv run pytest tests/unit/` → 1010 passed

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/auth/context_helper.py

@@ -54,8 +54,8 @@ def get_client_from_context(ctx: Context, base_url: str) -> NextcloudClient:
             raise ValueError("Username not available in OAuth token context")
 
         logger.debug(
-            f"Creating NextcloudClient for user {username} with multi-audience token "
-            f"(no exchange needed)"
+            "Creating NextcloudClient for user %s with multi-audience token (no exchange needed)",
+            username,
         )
 
         # Token was validated to have MCP audience
@@ -65,6 +65,6 @@ def get_client_from_context(ctx: Context, base_url: str) -> NextcloudClient:
         )
 
     except AttributeError as e:
-        logger.error(f"Failed to extract OAuth context: {e}")
+        logger.error("Failed to extract OAuth context: %s", e)
         logger.error("This may indicate the server is not running in OAuth mode")
         raise