v1.0.0

feat(v1.0.0): fork-on-delete + heatmap + true token counts (#4)

Major rewrite. Every `delete` now produces a NEW session file with a
fresh UUID instead of mutating the source. Output prints a
`claude --resume <new-id>` command. The new id forces a fresh prefix-
cache slot in Claude Code, so /context immediately reflects the
smaller size — no stale cache.

- delete: forks instead of mutating; output adds new_session_id,
  new_path, resume_command. Source file is never touched.
- heatmap: new subcommand. Ranks conversational turns by true token
  count (tiktoken on whole JSONL line — text + tool args + tool
  stdout + metadata). Drop the heaviest first.
- info / show: token counts now reflect wire size (typically 2-3x
  the old text-only estimate).
- list / search: forked files are tagged with a cc-session-fork
  sentinel line and surface as is_fork=true with an [edited] title
  prefix.
- Removed: --force flag, lsof concurrent-open detection, .bak
  backup, restore subcommand. None are needed when the source is
  never mutated.
- AGENTS.md: agent guide moved out of source into a real markdown
  file at the repo root. `cc-session agent-guide` reads it via
  include_str! so GitHub renders it natively and the binary stays
  self-contained.
- v1.0.0 bump.