fix: load tmux config from symlink and honor set -q

[teng-lin]

Fixes #67.

rmux silently ignores a standard oh-my-tmux install when used as the tmux-config fallback, and — once the config does load — startup hangs ~20s. Three independent issues, fixed in three commits.

1 — set -q is parsed but discarded

oh-my-tmux uses set -q -g status-utf8 on / setw -q -g utf8 on for options removed in newer tmux. tmux’s -q suppresses “unknown/ambiguous option” errors; rmux parsed -q and threw it away, so those lines raised invalid option: status-utf8. A single config error discards the entire file, so the whole config was dropped.

Now -q is captured into SetOptionFlags.quiet and suppresses unknown/ambiguous-option errors from resolve_set_option_scope (returning a no-op), matching tmux.

2 — the tmux-fallback reader rejects all symlinks

read_tmux_compat_source_entry used symlink_metadata + O_NOFOLLOW and rejected any symlink. Because the fallback path is best-effort, the error is swallowed — no message, no config. oh-my-tmux installs ~/.config/tmux/tmux.conf as a symlink, so it was silently skipped.

The symlink hardening (commit 2fd8872) was only meant to avoid blocking on a symlink→FIFO. Now the reader follows symlinks but stats the target (fs::metadata, which never blocks on a FIFO) to still skip FIFOs/dirs/devices, and keeps O_NONBLOCK as a second guard.

3 — a slow config run-shell freezes startup

Config run-shell commands run synchronously during startup config load, and the config-loading guard they hold gates client readiness. A command that blocks therefore makes rmux startup hang until the client’s 20s deadline. oh-my-tmux triggers this: its TMUX_PROGRAM detection / _apply_configuration shell out to the tmux binary against rmux’s socket and stall ~20s.

The daemon now releases the readiness guard after a short budget (2s) while the config keeps executing in the background — so a slow command no longer blocks startup. Normal configs finish far inside the budget and are never delayed; execution is not cancelled, so commands still complete and nothing is orphaned.

Verification

Real symlinked oh-my-tmux: startup drops from ~20s (hang) to ~2s, exit 0, options applied:

base-index 1   pane-base-index 1   history-limit 5000
escape-time 10   renumber-windows on   monitor-activity on

A plain rmux config still starts in ~0.02s (budget never triggers).

Tests

• tmux_best_effort_source_follows_symlink_to_regular_file — symlink→regular-file is loaded.
• startup_readiness_clears_before_a_blocking_run_shell_finishes — readiness clears before a blocking run-shell finishes (asserts the load task is still running, so it genuinely exercises the budget path).
• Existing tmux_best_effort_source_skips_symlink_to_fifo_without_blocking still passes.
• Full suites green: rmux-server (1648) and rmux-core (77); clippy clean.

Out of scope

Full oh-my-tmux theming still won’t work — it depends on the tmux binary via $TMUX_PROGRAM (re-detected via lsof, which rejects rmux’s internal daemon binary) and a deep _apply_configuration pipeline of bare tmux/rmux subcommands. This PR makes rmux load the config’s plain options and not hang; full oh-my-tmux compat is a separate effort tracked in #67.