Business needs as a checkable spec: needs.yaml + question_lint pass

A content repo may now state what the business needs the site to do,
apart from how the pages word it. question_lint checks each need
against the pages and aggregates.yaml:

- a path of submissions gets the answer into `lands_in`, within
  `max_steps` and a required-field budget (`max_fields`);
- `handled_by` holds a desk over that bucket;
- every `done_when` state is reachable through the moves that desk
  (or a self_transition) offers, and no record strands on the way;
- a disabled alternative is named as the reason when it is one;
- `planned: true` reports the gap as a warning instead of failing.

Personas - visitors in their own words - become typed `choice` tasks
(the page's question, its alternatives as the options) written as
JSONL by `--needs-tasks` (`--skim`: headings only). Any external
answering engine returns `{id, choice, confidence}` lines, graded by
`--needs-score [--min-accuracy]`: a misroute is a wording defect. The
engine stays outside this crate on purpose so classifiers and LLMs
can be compared on the same tasks. The runtime never reads the file.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L4jrCgLiKKHAEFuZUJjckH

src/lib.rs

@@ -13,6 +13,9 @@ pub mod aggregates;
 #[cfg(feature = "ssr")]
 pub mod announce;
 
+#[cfg(feature = "ssr")]
+pub mod needs;
+
 #[cfg(feature = "ssr")]
 pub mod server;