fix: Windows daemon.addr flock — separate lock from info file

PIP-003: Ed25519 checkpoint signing + trust layer architecture

ci: expand release matrix to 6 platforms

Add aarch64-linux-gnu, x86_64-linux-musl, and aarch64-apple-darwin
targets to match punkgo-jack's release workflow.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

fix: clippy unused import, cargo fmt

Co-Authored-By: Claude Opus 4.6 <[email protected]>

style: cargo fmt + update Cargo.lock for v0.2.9

Co-Authored-By: Claude Opus 4.6 <[email protected]>

fix: separate README for each crate, remove cross-badge confusion

- punkgo-core gets minimal README pointing to punkgo-kernel
- punkgo-kernel README drops punkgo-core badge
- Bump to v0.2.8

Co-Authored-By: Claude Opus 4.6 <[email protected]>

chore: add readme/keywords/categories for crates.io, bump to v0.2.7

- Point both crates to root README.md for crates.io display
- Add keywords and categories
- Fix import ordering (cargo fmt)

Co-Authored-By: Claude Opus 4.6 <[email protected]>

chore: add version to punkgo-core path dep for crates.io publish

Co-Authored-By: Claude Opus 4.6 <[email protected]>

feat: two-layer energy model — observe pays append_cost (v0.2.5)

Energy cost split into action_cost (operation semantics) + append_cost
(physical recording cost). Observe action_cost remains 0, but all actions
including observe now pay append_cost (1 + payload_bytes/1024). This
reflects the Landauer principle: recording to the Merkle tree has
irreducible physical cost regardless of action type.

- action.rs: quote_cost returns action_cost + append_cost
- kernel.rs: remove observe exemption from energy reservation
- Tests updated for +1 append_cost on all actions

Co-Authored-By: Claude Opus 4.6 <[email protected]>

feat: remove kernel.lock, default state dir to ~/.punkgo/state

- Remove file-based kernel.lock from StateStore; SQLite WAL handles
  concurrent access and IPC endpoint binding prevents duplicate daemons.
  Eliminates stale lock files after crashes.
- Change KernelConfig default state_dir from ./state to ~/.punkgo/state
  with PUNKGO_STATE_DIR env var override for custom deployments.
- Bump version to 0.2.4.

Co-Authored-By: Claude Opus 4.6 <[email protected]>