fix: enable uvx/PyPI deployments without Docker assumptions

Two bugs made `uvx --from . nextcloud-mcp-server run` (and any pip install)
unusable outside Docker:

1. Dynaconf was configured with ignore_unknown_envvars=True and relied on
   settings.toml to declare the key schema. With no settings.toml in a wheel
   install, every env var (NEXTCLOUD_HOST, MCP_DEPLOYMENT_MODE, ...) was
   silently dropped. Moved the schema into a Python _DEFAULTS dict passed
   directly to Dynaconf, kept settings.toml as an optional external override
   (renamed to settings.toml.example, gitignored), and pointed docker-compose
   at the example file.

2. Token SQLite DB defaulted to /app/data/tokens.db in multiple places
   (auth/storage.py, migrations.py, alembic/env.py, cli.py db subcommands),
   which blew up at uvicorn startup with FileNotFoundError on non-Docker
   hosts. Replaced with a new config.get_token_db_path() helper that
   resolves TOKEN_STORAGE_DB if explicitly set, otherwise allocates a
   per-process tempfile cleaned up at interpreter exit via atexit — mirroring
   the "ephemeral by default" pattern used for QDRANT_LOCATION=:memory:.

Containers are unaffected: docker-compose services now explicitly set
TOKEN_STORAGE_DB=/app/data/tokens.db (the fourth service that was missing
this pin has been brought in line with the other three).

Verified end-to-end in an isolated /tmp venv: env-var-only startup, Alembic
migrations run against the tempfile, Application startup complete, /health/live
returns 200, tempfile deleted on SIGTERM. Unit tests (464) + ruff + ty pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

alembic.ini

@@ -40,11 +40,12 @@ path_separator = os
 # Default: utf-8
 # output_encoding = utf-8
 
-# Database URL - can be overridden by:
-# 1. Passing -x database_url=... to alembic commands
-# 2. Setting in environment via get_database_url() in env.py
-# Default: sqlite:///app/data/tokens.db
-sqlalchemy.url = sqlite+aiosqlite:////app/data/tokens.db
+# Database URL - placeholder only.
+# Runtime code (migrations.get_alembic_config / alembic/env.get_database_url)
+# overrides this with config.get_token_db_path() which defaults to an
+# ephemeral per-process tempfile unless TOKEN_STORAGE_DB is set.
+# This value only matters for manual `alembic` invocations from the repo root.
+sqlalchemy.url = sqlite+aiosqlite:///./tokens.db
 
 [post_write_hooks]
 # Post-write hooks allow you to run scripts after generating migration files