Terminal: UTF-8-safe shared line editor, paste-leak containment, mid-line editing

[SkrawlCO]

TITLE: Terminal: UTF-8-safe shared line editor, paste-leak containment, mid-line editing

Depends on #485 (#485, "Terminal: decode parametrised/SS3 cursor keys, bracketed paste and lone ESC"). This branch is stacked on #485's commit; review or merge #485 first.

Problem

The terminal server has three separate line readers: BbsSession::readTelnetLine(), TelnetUtils::showInputDialog() and LineShell::readPromptLine(). Each implements editing differently:

• TelnetUtils::readRawChar() returns single bytes, so a UTF-8 character is split. In showInputDialog() its lead byte cancels the dialog; readPromptLine() silently drops it.
• Every reader returns at the first CR/LF and leaves the rest of a multi-line paste queued. Those lines then run as keystrokes against the next menu, prompt or password field.
• LineShell treats CR and LF as separate submits, so CRLF submits twice.
• Left/Right/Home/End are ignored in the boxed dialog, and the cursor is always drawn at end of text.

Impact

Non-ASCII input cancels dialogs or disappears, pasted text leaks into later prompts (including password fields), and CRLF clients double-submit.

Repair

• New telnet/src/TerminalLineEditor (codepoint-safe insert/delete, cursor motion, max length, submit/cancel) and TerminalLineHistory (per-prompt recall), shared by showInputDialog() and LineShell::readPromptLine().
• TelnetUtils::readRawChar() reassembles a UTF-8 lead byte and its continuation bytes into one character; truncated sequences don't hang.
• After a line is submitted or cancelled, BbsSession::drainPendingInput() discards input already queued from the same paste burst, so it cannot leak into the next prompt.
• CRLF is one submit, and bursts are coalesced so a paste redraws once.
• The boxed dialog honors cursor keys and draws the cursor at the insertion point, scrolling horizontally when needed.
• Both daemon include lists load the new classes, keeping the telnet and SSH include lists in sync.

Proof

• tests/Unit/TerminalLineEditorTest.php and tests/Unit/TerminalLineHistoryTest.php (pure unit tests).
• tests/Unit/TerminalLineInputPipelineTest.php: real BbsSession, TelnetUtils and LineShell readers over a socket pair. It covers:
  • UTF-8 preservation and codepoint-safe backspace;
  • multi-line paste containment;
  • CRLF;
  • Ctrl-C drain;
  • bracketed paste in every reader;
  • mid-line cursor editing and cursor placement;
  • password prompts masked with no history.
• 51 tests pass together with Terminal: decode parametrised/SS3 cursor keys, bracketed paste and lone ESC #485's TerminalKeyDecodingTest. Without this change the new classes are absent, so the tests cannot run. The rest of tests/Unit is unchanged.