* refactor: tighten LuaCATS annotations across modules
Problem: type annotations repeated inline unions with no aliases,
used `table<string, any>` where structured types exist, and had
loose `string` where union types should be used.
Solution: add `pending.TaskStatus`, `pending.RecurMode`,
`pending.TaskExtra`, `pending.ForgeType`, `pending.ForgeState`,
`pending.ForgeAuthStatus` aliases and `pending.SyncBackend`
interface. Replace inline unions and loose types with the new
aliases in `store.lua`, `forge.lua`, `config.lua`, `diff.lua`,
`views.lua`, `parse.lua`, `init.lua`, and `oauth.lua`.
* refactor: canonicalize internal metadata field names
Problem: `pending.Metadata` used shorthand field names (`cat`, `rec`,
`rec_mode`) matching user-facing token syntax, coupling internal
representation to config. `RecurSpec.from_completion` used a boolean
where a `pending.RecurMode` alias exists. `category_syntax` was
hardcoded to `'cat'` with no config option.
Solution: rename `Metadata` fields to `category`/`recur`/`recur_mode`,
add `category_syntax` config option (default `'cat'`), rename
`ParsedEntry` fields to match, replace `RecurSpec.from_completion`
with `mode: pending.RecurMode`, and restore `[string]` indexer on
`pending.ForgeConfig` alongside explicit fields.
939251f629
