feat(v1.0.0): fork-on-delete + heatmap + true token counts

[dudegladiator]

Major rewrite. Every delete now writes a NEW session file with a fresh UUID and prints a claude --resume <new-id> command. Source file is never touched. New session id forces a fresh prefix-cache slot in Claude Code, so /context immediately reflects the smaller size — no stale cache.

What changed

• fork-on-delete — delete produces new_session_id, new_path, resume_command. No more in-place mutation.
• heatmap subcommand — cc-session heatmap <id> ranks conversational turns by true token count (tiktoken on whole JSONL line: text + tool args + tool stdout + metadata).
• true token counts — info / show token numbers now reflect wire size (typically 2-3x the old text-only estimate).
• fork badge — list / search show is_fork=true with an [edited] title prefix.
• AGENTS.md — agent guide moved out of source into a real markdown file at the repo root, included via include_str!. GitHub renders natively; binary stays self-contained.

Removed

• --force flag, lsof concurrent-open detection, .bak backup, restore subcommand. None are needed when the source is never mutated.

Verified

• 62/62 unit tests pass (4 new for parentUuid relink, 2 new for fork sentinel, plus token-count tests for tool I/O)
• Smoke test on real session: 91e440c0 (639 msgs, 662k tokens) → fork 1d9a021d (319 msgs, 276k tokens). Resumed in Claude Code, /context dropped from 433k → 230k (47%)
• Sentinel line accepted by Claude Code's renderer (verified via fresh resume)