…t (Termux/Android arm64-musl)

bug #1 (cross-fork P0): codex remote-control fails on Termux with "lock()
not supported". Five-callsite Iter 1 fix because the codex-termux release
line is aarch64-unknown-linux-musl (so cfg!(target_os = "android") gates
are inactive on the affected binary):

- app-server-transport/src/transport/unix_socket.rs:
  acquire_app_server_startup_lock tolerates ErrorKind::Unsupported on
  file.lock(); production retry serialization preserved on Linux/Mac.
- core/src/installation_id.rs: replaced installation_id_lock_is_optional
  (gated cfg!(target_os = "android"), inactive on musl-linux release)
  with is_unsupported_file_lock_error (kind-based, runtime detection).
- message-history/src/lib.rs: try_lock() and try_lock_shared() callsites
  proceed without advisory locking on Unsupported; O_APPEND + sub-PIPE_BUF
  atomic writes keep lines intact.
- arg0/src/lib.rs: replace cfg!(target_os = "android") gate on two
  try_lock callsites (path-entry guard + try_lock_dir).
- execpolicy/src/amend.rs: append_locked_line tolerates Unsupported lock;
  dedup check at file scan reduces (but does not eliminate) the chance of
  duplicate appends on lockless filesystems.
- is_unsupported_file_lock_error helper + 2 unit tests added per crate.

bug #3 (cross-fork P1, GitHub issue #10 J3y0r): MCP servers spawned via
npx fail on Termux with "handshaking with MCP server failed: connection
closed: initialize response". rmcp-client/src/utils.rs:
create_env_for_mcp_server chains TERMUX_ENV_VARS (PREFIX, LD_PRELOAD,
NPM_CONFIG_PREFIX, ANDROID_*, XDG_*) when running_on_termux() detects
TERMUX_VERSION env var. Runtime detection because the Termux release line
is musl-linux. Empty allowlist on non-Unix targets to keep the
cross-target name resolution consistent. 2 new unit tests (propagate +
no-leak).

flaky test (cross-fork): transport::remote_control::tests::
remote_control_waits_for_account_id_before_enrolling timeout raised from
100ms to 950ms (below the 1s REMOTE_CONTROL_ACCOUNT_ID_RETRY_INTERVAL) to
remove the residual flake rate observed under CPU pressure on the Termux
release line. 25/25 PASS isolated post-fix.

Cargo.lock workspace version bump 0.133.1 -> 0.134.1 is auto-managed by
cargo during the develop checkout; included to keep the lock consistent.

Tests: 78 lib tests PASS across the affected crates. Test coverage added
(10+ new unit tests across the modified crates).