feat(query): uniform predicate negation — prefix ~ as a NOT wire node

[0x054]

Implements PRD #310 across both slices in one PR: the ~ tracer bullet on leaf predicates (#312) and compounds, guard rails, and docs (#313).

What

One universal negation rule: prefix ~ negates any predicate node — leaf comparison or AND/OR compound.

Txn.where(lambda t: ~t.category_id.in_(ids))          # NOT IN — previously unspellable
User.where(lambda u: ~u.email.like("%@example.com"))  # NOT LIKE — likewise
User.where(lambda u: ~((u.active == True) | (u.email.like("%@ferro.dev"))))

renders as a faithful NOT (...) over the child:

SELECT ... FROM "user" WHERE NOT ("category_id" IN (...))
SELECT ... FROM "user" WHERE NOT ("active" = TRUE OR "email" LIKE '%@ferro.dev')

How

• Python: QueryNode.__invert__ wraps any node in a NOT node; the truthiness guard (__bool__) now names ~ as the supported spelling. The mutate traversal guard and join registration see through NOT, so ~ can neither smuggle a join into update()/delete() nor drop a traversed child's join.
• Wire: a new recursive not node kind beside leaf/compound — {"node_kind": "not", "child": {...}}, any child, any depth. QueryIR version bumps to v6 (unconditional, single supported version; the Rust gate rejects v5 with the actionable one-wheel message). No per-operator negative forms anywhere (ADR-0008).
• Rust: one recursion case in the condition builder emitting SeaQuery Cond::not over the rebuilt child. Double negation reaches Rust as two nested not nodes; SeaQuery's negation toggle renders the even nesting as the plain child — semantically exact under three-valued logic (NOT NOT x ≡ x for TRUE/FALSE/UNKNOWN alike).
• Golden vectors: two hand-authored vectors pin the not-over-leaf and not-over-compound shapes, asserted byte-for-byte from the Python emitter and round-tripped by the Rust decoder; the existing query vectors move to v6.

Testing

• End-to-end result-set tests (tests/test_negation.py), green on both backends: ~ over every leaf operator kind (==, !=, orderings, in_, like), ~ over AND/OR compounds, double negation, ~ mixed into &/| trees at multiple levels, NULL-row behavior under negation (three-valued semantics, matching !=), composition with order_by()/limit(), and ~ over a relation-traversing leaf.
• Error paths: the truthiness-guard message pinned to name ~; NOT-wrapped traversal rejected on update()/delete().
• Full suite: 1599 passed on sqlite+postgres; all Rust workspace suites green.

Docs

New "Negating Conditions" guide section with the central three-valued-logic note (real nullable-column model in Assignment + Annotated tabs, rendered SQL); ~/NOT row in the operators table; API reference states the universal rule; not_in() removed from the roadmap. All examples lambda-style and runnable under the docs test harness.

Closes #312
Closes #313