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/context.py

@@ -139,7 +139,9 @@ def _get_client_from_basic_auth(ctx: Context) -> NextcloudClient:
         raise ValueError("Invalid BasicAuth credentials - missing username or password")
 
     logger.debug(
-        f"Creating multi-user BasicAuth client for {settings.nextcloud_host} as {username}"
+        "Creating multi-user BasicAuth client for %s as %s",
+        settings.nextcloud_host,
+        username,
     )
 
     # Create client that passes BasicAuth credentials through to Nextcloud
@@ -191,7 +193,7 @@ async def _get_client_from_login_flow(
 
     username = app_data.get("username") or user_id
 
-    logger.debug(f"Creating Login Flow v2 client for {nextcloud_host} as {username}")
+    logger.debug("Creating Login Flow v2 client for %s as %s", nextcloud_host, username)
 
     return NextcloudClient(
         base_url=nextcloud_host,