chore: drop the unreachable duplicates in denial_reason() (#151)

[ifahimreza]

Closes #151

What

Deletes 19 unreachable lines at the end of Saddle_Capabilities::denial_reason().

Why

The function ended with verbatim copies of two branches it had already run:

• The second domain-drift condition is character-identical to the first. If it were true, the function already returned saddle_domain_drift.
• The second tier-denied condition is character-identical to the first. If it were true, the function already returned saddle_insufficient_scope or saddle_tier_denied — that block has no fall-through path.
• $required is assigned before both, and nothing between them touches it, $gate, or any state either condition reads.

This is worth deleting rather than ignoring, because the duplicate tier block is a worse version of the one that runs — it omits the saddle_insufficient_scope branch. If it ever became reachable it would tell an OAuth-scope-limited agent to go raise the site's access level, which is the wrong screen, and is exactly the bug #108 fixed. A stale copy of a corrected code path sitting next to the corrected one is how that regression comes back.

Found while reading denial_reason() for #148, and kept out of that PR so the security diff stays reviewable.

Testing

• composer test — 612 tests, unchanged. No new test: unreachable code cannot change behaviour, and the proof nothing moved is capabilities-test.php's existing gate-ordering coverage staying green.
• composer lint — 0 errors
• php -l clean

CI note: main is red on Saddle_Skills_Test::test_the_playbook_adapts_step_two_to_a_classic_theme (#145, CI-only, green locally). This branch inherits it; unrelated to this diff.

[ifahimreza]

CI: red on the inherited #145 failure only.

Tests: 612, Assertions: 2410, Failures: 1 — Saddle_Skills_Test::test_the_playbook_adapts_step_two_to_a_classic_theme, which is #145. Assertion count is unchanged from main, which is the expected result for deleting unreachable code. PHPCS passes.

Not claiming green.