Prepare v0.7.0 and remove legacy identity-key migration

[hwbehrens]

Description

This PR includes the full usability work from commit 1e1ff5ce0f5642b82400557ac6ab29fbb25716db plus follow-up hardening/release updates.

Included change sets

1) Usability improvements v2 (commit 1e1ff5c)

Implement usability improvements v2 for CLI, IPC, and pairing events

Scope: 35 files changed, 1673 insertions, 314 deletions.

Highlights:

• CLI UX and contracts:
  • Added/expanded CLI helper modules for formatting, IPC client behavior, identity output, notify payload handling, and config command handling.
  • Added axon config command surface and tests (axon/src/cli/config_cmd.rs, axon/src/cli/config_cmd_tests.rs, axon/tests/cli_contract_config.rs).
  • Updated top-level CLI wiring and behavior (axon/src/main.rs, axon/src/main_tests.rs, axon/tests/cli_contract.rs).
• IPC / daemon / transport behavior:
  • Updated IPC protocol and server handling (axon/src/ipc/protocol.rs, axon/src/ipc/server.rs, axon/src/ipc/server_tests.rs).
  • Updated daemon command handling and lifecycle wiring (axon/src/daemon/command_handler.rs, axon/src/daemon/mod.rs).
  • TLS/pairing-event related improvements and tests (axon/src/transport/tls.rs, axon/src/transport/tls_tests.rs).
• Documentation/spec updates for the above behavior:
  • README.md, spec/IPC.md, spec/SPEC.md

2) Rubric-finding fixes

• Corrected AGENTS metadata drift (CLI subcommands and config format wording).
• Fixed fuzz coverage wiring:
  • renamed config fuzz target to YAML-oriented target
  • aligned fuzz dependency from TOML to YAML parser
  • included all declared fuzz targets in make fuzz (including fuzz_ipc_session)

3) Release prep and invariants

• Bumped crate version to 0.7.0:
  • axon/Cargo.toml
  • axon/Cargo.lock (root package entry)
• Enforced file-size invariant by splitting an oversized test file; all Rust source files are now under 500 lines.

4) Legacy identity migration removal

• Removed legacy/raw identity.key auto-migration paths.
• Identity loading is now strict base64-only for 32-byte seed material.
• doctor now treats legacy raw/non-UTF-8 identity key files as unrecoverable unless --fix --rekey is used.
• Updated tests/docs/spec accordingly.

Verification

• make verify passes.
• Rust file line-limit check passes (max observed: 498 lines).

Self-Assessment Score

Score: 94/100

(Per request, this is the prior/outdated rubric score included for CONTRIBUTING compliance.)