fix: P2 bundled diagnostic improvements from rerun7

[danieljohnmorris]

Summary

Three rerun7 P2 diagnostic / scripting fixes in one PR. Each is small, isolated, and addresses a specific persona-reported false-positive or missing hint.

1. \x{body} Haskell/Rust lambda shorthand hint (quant-trader rerun7) - lexer hits \ followed by ident-then-{ (or ->) and emits ILO-L001 pointing at the canonical parenthesised lambda (x:t>r;body). Manifesto win: persona's first retry is the right shape.
2. Precedence-pair hint dedupe (content-mod, ab-tester, logs-forensics, scientific-researcher rerun7) - detect_prefix_precedence_trap was suppressed inside (...) but still spammed [*/a b c] and brace-bodied uses with self-contradictory advice. Extend the immediate-predecessor suppression list to include LBracket and LBrace alongside LParen.
3. ensure-ilo.sh direction swap (streaming-tail rerun7) - the script used string-equality only for version compare. A dev build ahead of the published release (local 0.11.6 vs published 0.11.5) hit the not-equal branch and tried to "Update from 0.11.6 to 0.11.5". Now uses sort -V to skip the upgrade when local is newer.

Repro before / after

Item 1:

$ ilo run /tmp/lam.ilo  # f xs:L n>L n;map \x{+x 1} xs
# before
error: unexpected token '\'   suggestion: Unexpected character(s): '\'
# after
error: unexpected token '\'   suggestion: `\x{body}` is a Haskell/Rust lambda shorthand.
                              ilo lambdas are parenthesised: `(x:t>r;body)`...

Item 2:

$ ilo run /tmp/list.ilo  # f a:n b:n c:n>n;hd [*/a b c]
# before
hints: ["hint: `*/a b c` parses as `(a/b)*c` ..."]   # false positive
# after
(silent — bare `*/a b c` after `;`/`=`/etc still fires correctly)

Item 3:

$ ensure-ilo.sh  # local 0.11.6, published 0.11.5
# before
Updating ilo from 0.11.6 to 0.11.5...   # downgrade!
# after
ilo is ahead of the published release (0.11.6 > 0.11.5), keeping local build

What's in the diff (per commit)

• lexer: hint at parenthesised lambda for \x{body} shorthand - new backslash_lambda_hint helper, detection at the L001 site, five regression tests (brace, arrow, space-param, lone backslash, ident-no-brace fallback). SPEC.md gets the entry in the Cross-language gotchas table (mirrors into ai.txt and SKILL.md via build.rs). SKILL.md numbered gotchas list gets entry 8a. New examples/backslash-lambda-hint.ilo runs across every engine via the example harness.
• main: suppress prefix-precedence hint inside [ and { grouping - one-line extension of the predecessor match in detect_prefix_precedence_trap. Three regression tests cover bracket-grouped at all four pair shapes, nested paren-inside-brackets, and a unit-level pin for both new openers.
• scripts: skip ensure-ilo upgrade when local is newer than published - sort -V comparison after the equality check.

Test plan

• cargo test --release --features cranelift - all 351+ tests pass
• cargo clippy --release --features cranelift -- -D warnings - clean
• cargo fmt --check - clean
• Manual repro: each of the three before/after scenarios verified against the release binary
• Example harness runs the new backslash-lambda-hint.ilo across every engine (tree, VM, Cranelift)
• Existing precedence-trap regression tests (paren-grouped, bare, infix, etc.) still pass

Follow-ups

None. Each fix is self-contained.

[codecov]

Codecov Report

❌ Patch coverage is 98.13084% with 2 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/lexer/mod.rs	97.36%	2 Missing ⚠️

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