fix(interpreter): match bash stderr for set -x, syntax errors and TIMEFORMAT

[chaliy]

Requested by Михайло · project thread

What changed

• set -x quotes traced words like bash, traces assignments, function calls, eval/source and [[ ]] terms, expands PS4 and repeats its first char per $(...)/eval/source/trap level. Trace lines are ordered with pending $(...) stderr.
• Parse errors use bash wording: "syntax error near unexpected token T'" plus the source line, "unexpected end of file", "unexpected EOF while looking for matching". Reports are named bash: -c, the script path, $0: evalor the sourced file via newError::syntax_report`.
• time honors TIMEFORMAT (%[p][l]R, %%; CPU fields print unavailable).
• [[ ! a || b ]] negates only a; $LINENO in [[ ]]/(( )) keeps the enclosing line; bash/sh children apply their redirects to their own errors.

Why

Level-up roadmap, fidelity step: stderr text was the main remaining gap in the bash oracle.

Before / After (verified)

bash-oracle strict: 94 → 99 / 106 (match stays 101). floor.txt raised to 101 99.

Script set -x; x="a b"; echo "$x" 'it''s'; y=$(echo hi) plus bash -c 'if then fi', stderr from bash 5.2 and this branch is identical:

+ x='a b'
+ echo 'a b' its
++ echo hi
+ y=hi
bash: -c: line 1: syntax error near unexpected token `then'
bash: -c: line 1: `if then fi'

Before, traces were unquoted with no assignment lines, and parse errors used bashkit's own parser wording.

Risk

• Error::syntax_report is new public API.
• Remaining gaps documented in knowledge/operations/limitations.md (no trace of for/case/select headers, <(...), some parse errors keep bashkit wording).
• Stack use checked against main for the coverage job (branch 1,893,376 vs main 1,909,696 bytes).

Checklist

• Failing tests first (xtrace.test.sh, parse-errors.test.sh, time.test.sh), verified against bash 5.2
• fmt, clippy, integration, lib, CLI, bash_comparison
• knowledge updated (log, limitations, parser)

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