Introduces `src/profile.rs`: a `Profile` bundles param/metric declarations
plus a placeholder dashboards field, and `ProfileStore` persists all
profiles as a single profiles.json file, resolved relative to the settings
file's directory (same convention as ticket 010's CSS storage). Adds CRUD
(create/list/get/delete/set_active) that keeps Settings.profiles.names and
active_profile in sync, plus record_param_declaration/record_metric_declaration
hooks that ticket 004's HTTP API will call to persist newly-declared
params/metrics into the active profile.
Wires main.rs to replay the active profile's declarations into the engine
before spawning the ingest task, so backfill/live-derivation semantics
apply uniformly to every ingested line.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o
