_detect_prompt_suffix accepted ANY line ending in $#%> as a PS1 prompt,
so a single `cat /var/log/dpkg.log` (195 lines closing in `<none>`)
flooded environmental.shell_type votes and flipped a plainly-bash
session to fish.
A prompt line now requires either a trailing space after the suffix
(default PS1 shape across bash/zsh/fish/PowerShell) or a PS1-shape
token (user@host, "PS " prefix, or a Windows drive-letter prefix).
Regression tests pin the dpkg.log false-positive and a $-terminated
prose line.
Adds PromptLine dataclass + extract_prompt_lines() helper. PromptLine
carries ts, suffix_char ($/#/%/>), raw_line (ANSI-stripped, capped),
is_root flag. Populated during the existing single-pass output-window
walk; SessionContext gains prompt_lines, Command gains
followed_by_prompt.
PII trade-off (ANTI-authorised at Phase F): PS1 text retained on ctx
so F.1 / F.3 / E.4 can read it. Capped at PROMPT_LINE_MAX_CHARS=256.
Observations still only carry derived primitive values.
D.0's regex error helpers stay alongside (NOT subsumed) — they fire
even when PS1 echo is suppressed. F.0 enriches D.0 rather than
replacing it.
