[tonicmuroq]

Claim events now carry template and size from the claim's pool key, in the journal line and as two new columns of sandboxd_usage.

A consumer that prices compute by sandbox shape (e.g. 4c8g vs 8c16g, or by the platform the template implies) can only get the shape from the claim record today, and that record is gone after release. key is a hash, so it can't be mapped back. With the shape on the claim event, the usage stream alone is enough to price a sandbox.

• usage.Event: template, size (omitted when empty; only claim events set them)
• sandboxd_usage: template, size text columns, NOT NULL DEFAULT ''
• docs: journal fields in sandboxd-api.md, DDL in deploy.md

Upgrade note: sandboxd_usage is only created when missing, so a table made by a pre-release build of #407 needs the columns added by hand before this runs. Until then landing fails and GET /v1/usage answers 503. The journal itself is unaffected and catches up after the ALTER, for lines still in usage.jsonl and its .1 backup:

ALTER TABLE sandboxd_usage
    ADD COLUMN IF NOT EXISTS template text NOT NULL DEFAULT '',
    ADD COLUMN IF NOT EXISTS size     text NOT NULL DEFAULT '';