fix(hooks): honor exclude_commands for head/tail line-range fast path

[AZERDSQ131]

Closes #2823

[hooks] exclude_commands is bypassed for head/tail because the line-range fast path in rewrite_segment_inner returns before the exclusion check:

if cmd_part.starts_with("head -") || cmd_part.starts_with("tail ") {
    return rewrite_line_range(cmd_part).map(|r| format!("{}{}", r, redirect_suffix));
}

is_excluded is only consulted in the Classification::Supported and Unsupported arms further down, both downstream of this early return.

Repro before this fix (config: [hooks] exclude_commands = ["tail", "head", "rg"]):

$ rtk rewrite "tail -3 sample.txt"
rtk read sample.txt --tail-lines 3     # rewritten despite the exclusion

Fix: moved the same is_excluded check the Supported arm already uses (ENV_PREFIX-stripped command matched against the configured ExcludePattern list) in front of the fast path's early return, so excluded head/tail invocations fall through to the raw-passthrough path like every other excluded command.

Adds three regression tests in src/discover/registry.rs:

• test_exclude_tail_line_range_fast_path — excluded tail no longer rewrites
• test_exclude_head_line_range_fast_path — excluded head no longer rewrites
• test_head_line_range_fast_path_still_rewrites_when_not_excluded — guards against fixing this by disabling the fast path entirely

Ran the mandatory gate locally:

• cargo fmt --all — no changes needed
• cargo clippy --all-targets — clean
• cargo test --all — 2396 passed (+ 6/11/11/14/5/11 in the other suites), 0 failed

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