Add Seal of Reliability properties to schema

[Alessandro100]

Add the decided properties to best represent the seal of reliability to the schema

!important: we must really get on top of naming because once it's in the schema its going to be harder to change

[jcpitre]

The suggestion is to create two new tables that aggregate all information relating to the seal of reliability.
See #1761 for the usage of these tables.

New Tables

The feed_reliability_seal and seal_criterion tables intentionally denormalize data already present in gtfs_feed_availability_check, validationreport, and gtfsdataset. This follows the same pattern already used in this codebase (e.g. gtfsfeed.latest_dataset_id): raw tables are the source of truth and append-only; the seal tables are a nightly-computed cache that lets the API answer "does this feed have the seal?" in a single row lookup with no joins.

feed_reliability_seal holds one row per feed and owns the overall seal outcome. seal_criterion holds one row per feed per criterion (six rows per feed) and owns all per-criterion state. Out of scope for this issue, but this would make adding (or removing) some criteria in the future easier and maybe qualify a given criterion, e.g. having an experimental flag.

CREATE TABLE feed_reliability_seal (
   feed_id        VARCHAR(255) PRIMARY KEY
                      REFERENCES gtfsfeed(id) ON DELETE CASCADE,

   has_seal       BOOLEAN NOT NULL DEFAULT FALSE,
   seal_earned_at TIMESTAMPTZ,
   seal_lost_at   TIMESTAMPTZ,

   created_at     TIMESTAMPTZ NOT NULL DEFAULT NOW(),
   updated_at     TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

CREATE TYPE seal_criterion_name AS ENUM (
   'official',
   'stable',
   'available',
   'compliant',
   'fresh_coverage',
   'fresh_continuous'
);

-- raw_* columns reflect the instantaneous state at the last evaluation, with no grace applied.
-- grace_* columns reflect the debounced state: a failure is only confirmed after its grace period expires.
-- The seal logic is driven exclusively by grace_* columns; raw_* columns are for monitoring and audit.
CREATE TABLE seal_criterion (
   feed_id                        VARCHAR(255) NOT NULL
                                      REFERENCES gtfsfeed(id) ON DELETE CASCADE,
   criterion                      seal_criterion_name NOT NULL,

   -- Current state
   raw_failing                    BOOLEAN,      -- NULL = not yet evaluated; TRUE = failing at last check, no grace applied
   grace_failing                  BOOLEAN,      -- NULL = not yet evaluated; TRUE = failure has persisted beyond the grace period

   -- Evaluation tracking
   evaluated_at                   TIMESTAMPTZ,

   -- Failure tracking
   first_raw_failure_at           TIMESTAMPTZ,  -- start of current raw failure streak; cleared on recovery
   last_raw_failure_at            TIMESTAMPTZ,  -- end of last raw failure streak: never cleared
   last_grace_failure_at          TIMESTAMPTZ,  -- end of the grace period failure; never cleared

   created_at                     TIMESTAMPTZ NOT NULL DEFAULT NOW(),
   updated_at                     TIMESTAMPTZ NOT NULL DEFAULT NOW(),

   PRIMARY KEY (feed_id, criterion)
);