feat: support arbitrary TOML sections and wildcard schema keys

[teal-bauer]

Two related changes that unblock adding new top-level sections and shrink the schema's footprint for indexed data.

Arbitrary sections

BurntSushi/toml silently drops top-level table keys that don't match a struct field, so adding a new [profiles] or [fleet] section to /data/settings.toml made those settings vanish on every save cycle. Replace the hardcoded Config struct with map[string]map[string]interface{} so every top-level section round-trips.

As a side effect, service.go no longer needs its hardcoded-prefix warning. Replaced with schema.Has(field) so "this field isn't declared in the schema" logs come from the schema, not a literal list in code. Fields are still persisted regardless.

Wildcard schema keys

Schema keys can now contain * segments:

"dashboard.saved-locations.*.latitude": {
  "type": "float",
  "min": -90,
  "max": 90
}

Matches any single segment, so dashboard.saved-locations.42.latitude resolves the same way. Exact-match entries take precedence over patterns on collision. Parse splits entries into Settings (exact) and Patterns (wildcard) at load time so Lookup and Has stay O(1) for the common case.

Converted the five existing dashboard.saved-locations.0.* placeholder entries to .*. form, and dropped the pattern: "indexed" annotation that was standing in for the missing wildcard support.

Scope

On-disk TOML format is unchanged (still quoted flat keys like "saved-locations.0.latitude" under [dashboard]). Nested sub-tables are #3's job. Redis hash settings is unchanged; every field still lives there. Existing sections, keys, and defaults behave identically.

Test plan

• go build ./... passes
• go test ./... passes
• Round-trip: arbitrary [fleet], [profiles] sections serialize to TOML and flatten back to dotted Redis keys
• Wildcard lookup: dashboard.saved-locations.0.latitude and dashboard.saved-locations.42.latitude both match the .*.latitude schema entry
• Deploy to deep-blue, confirm no regression in existing settings