fix(tools): align claude-memory insert with memory_20250818 line semantics

[rohitsux]

Problem

Anthropic's memory_20250818 tool spec defines the insert command as: insert_text is inserted after line insert_line, 0 inserts at the beginning of the file, and the valid range is [0, n_lines].

ClaudeMemoryTool.insert treated insert_line as a 1-based insert-before index with range [1, n_lines + 1]:

if (insertLine < 1 || insertLine > lines.length + 1) { ... }
lines.splice(insertLine - 1, 0, insertText)

The caller of this tool is Claude itself, which is trained on the spec semantics, so in practice:

• every model-driven insert landed one line earlier than intended,
• insert_line: 0 (insert at top of file) was rejected as invalid,
• insert_line: n_lines (append) inserted before the last line instead of after it.

Same class of issue as #1285 (str_replace spec literalness), one command over.

Fix

Validate against [0, lines.length], splice at insert_line directly (0-based insert-after), and update the error and success messages to the spec's wording. One existing tool-operations test encoded the old insert-before behavior; its insert_line is adjusted from 2 to 1 so its expected output stays byte-identical under spec semantics.

Tests

New insert line semantics describe block in claude-memory.test.ts using the existing mock harness: top-of-file (insert_line: 0), middle insert-after, append at n_lines, and both out-of-range directions (negative and n_lines + 1, asserting no write occurs). All four fail on main and pass with the fix.

Verification

• bun run test claude-memory: 14 passed (10 existing + 4 new).
• Full packages/tools suite: 87 passed, zero new failures (the two pre-existing file-level failures reproduce identically on unmodified main).
• bun run build clean.

Scope

Only the insert command's line-index semantics change (validation range, splice index, and its two messages). str_replace, view, create, delete, and rename are untouched.