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/observability/metrics.py

@@ -231,14 +231,15 @@ def setup_metrics(port: int = 9090) -> None:
     """
     try:
         start_http_server(port)
-        logger.info(f"Prometheus metrics server started on port {port}")
+        logger.info("Prometheus metrics server started on port %s", port)
     except OSError as e:
         if "Address already in use" in str(e):
             logger.warning(
-                f"Metrics port {port} already in use (metrics server likely already running)"
+                "Metrics port %s already in use (metrics server likely already running)",
+                port,
             )
         else:
-            logger.error(f"Failed to start metrics server on port {port}: {e}")
+            logger.error("Failed to start metrics server on port %s: %s", port, e)
             raise