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/vector/placeholder.py

@@ -122,13 +122,19 @@ async def write_placeholder_point(
         )
 
         logger.debug(
-            f"Wrote placeholder for {doc_type}_{doc_id} (user={user_id}, "
-            f"modified_at={modified_at})"
+            "Wrote placeholder for %s_%s (user=%s, modified_at=%s)",
+            doc_type,
+            doc_id,
+            user_id,
+            modified_at,
         )
 
     except Exception as e:
         logger.error(
-            f"Failed to write placeholder for {doc_type}_{doc_id}: {e}",
+            "Failed to write placeholder for %s_%s: %s",
+            doc_type,
+            doc_id,
+            e,
             exc_info=True,
         )
         raise
@@ -180,7 +186,9 @@ async def query_document_metadata(
         return None
 
     except Exception as e:
-        logger.warning(f"Error querying document metadata for {doc_type}_{doc_id}: {e}")
+        logger.warning(
+            "Error querying document metadata for %s_%s: %s", doc_type, doc_id, e
+        )
         return None
 
 
@@ -219,11 +227,16 @@ async def delete_placeholder_point(
             ),
         )
 
-        logger.debug(f"Deleted placeholder for {doc_type}_{doc_id} (user={user_id})")
+        logger.debug(
+            "Deleted placeholder for %s_%s (user=%s)", doc_type, doc_id, user_id
+        )
 
     except Exception as e:
         logger.error(
-            f"Failed to delete placeholder for {doc_type}_{doc_id}: {e}",
+            "Failed to delete placeholder for %s_%s: %s",
+            doc_type,
+            doc_id,
+            e,
             exc_info=True,
         )
         raise
@@ -271,13 +284,16 @@ async def update_placeholder_status(
         )
 
         logger.debug(
-            f"Updated placeholder status for {doc_type}_{doc_id} to '{status}' "
-            f"(user={user_id})"
+            "Updated placeholder status for %s_%s to '%s' (user=%s)",
+            doc_type,
+            doc_id,
+            status,
+            user_id,
         )
 
     except Exception as e:
         logger.warning(
-            f"Failed to update placeholder status for {doc_type}_{doc_id}: {e}"
+            "Failed to update placeholder status for %s_%s: %s", doc_type, doc_id, e
         )
         # Don't raise - status updates are non-critical