fix(auth): make advisory locks dialect-aware and harden SQLite DSN

[localai-bot]

Fixes #10506.

Two failures hit deployments that use the default SQLite auth database (LOCALAI_AUTH=true without LOCALAI_AUTH_DATABASE_URL=postgres://...):

1. no such function: pg_advisory_lock on SQLite

core/services/advisorylock executed PostgreSQL-only SQL (pg_advisory_lock / pg_try_advisory_lock / pg_advisory_unlock) unconditionally. The auth DB can be SQLite, so the job store, agent store and node registry migrations failed with migrating job tables: advisorylock: acquiring lock 105: no such function: pg_advisory_lock (non-fatal in standalone startup, fatal in distributed mode).

WithLockCtx / TryWithLockCtx now branch on the gorm dialect:

• PostgreSQL keeps the existing cross-process advisory lock (byte-for-byte unchanged).
• SQLite / any other dialect uses a context-aware, per-key in-process lock (buffered-channel mutex). A SQLite auth DB is effectively single-process, so serializing guarded sections within the process is sufficient; we cannot and need not coordinate across processes the way a PG advisory lock does.

2. database is locked over network storage

The SQLite auth DSN set no busy timeout, so transient SQLITE_BUSY over network-backed storage (SMB/CIFS/NFS, e.g. Azure Files / Azure Container Apps) failed AutoMigrate immediately with failed to migrate auth tables: database is locked (the reporter's Azure case).

buildSQLiteDSN now sets _busy_timeout=5000 and _txlock=immediate (caller-supplied values preserved). WAL is intentionally not enabled - its shared-memory mmap does not work over network filesystems, which is the failing environment. Docs note that PostgreSQL should be used when the data directory lives on shared storage.

Tests

• New non-Docker SQLite specs for advisorylock: executes under lock, serializes concurrent goroutines on the same key, returns error on already-cancelled context, and TryWithLockCtx returns (false, nil) when the key is held.
• buildSQLiteDSN unit tests: plain path, :memory:, pre-existing query string, and no-override of caller-supplied pragmas.
• Existing PostgreSQL advisorylock testcontainer specs and the auth InitDB SQLite test still pass.

Verification

gofmt clean; go vet clean (with and without -tags auth); full advisorylock suite incl. Postgres testcontainers green; auth DSN + InitDB tests green; golangci-lint --new-from-merge-base=origin/master reports 0 issues.

Assisted-by: Claude:claude-opus-4-8 [Claude Code]