[DWAA1660]

Fixes #111. A quoted CSV value such as first line\nsecond line previously became two Markdown table rows after save/reopen; HTML folded its newline into a space. Both page formats now keep the value in one cell with its original line endings.

Table cell text uses <br> for LF and optional data-nc-break="crlf" / data-nc-break="cr" attributes for CRLF/CR, preserving the exact value without normalizing the imported data. The Markdown reader enables these breaks only inside table cells. Literal break-tag text and inline code remain literal; paragraph serialization is unchanged. The representation is documented in the folder-format guide.

Validation:

• The original LF regression failed before implementation. An additional CRLF/CR probe exposed HTML whitespace loss; the extended regression failed before that was fixed too.
• cargo test -p notecraft-formats: passed, including whole-demo format parity. Regressions cover repeated round trips in both formats, mixed, leading, trailing and repeated line breaks, Unicode, pipes, literal markup, backticks and backslashes, plus unchanged paragraph/code controls.
• cargo xtask ci: passed after the final edit; mandatory commit/push hooks also passed the full gate.
• cargo build --workspace --locked: passed on Windows.
• Actual off-screen NoteCraft app captures reviewed for HTML and CMGFM at 1440x900, 1x, light-default: the table has two text lines in one row in both. LF and CRLF captures are byte-identical within each format. No golden screenshots committed.
• All 10 GitHub PR checks passed on head 05a8ee3932fb83073a0db28cc70f462566257e39, including Linux/Windows/macOS build/tests, WASM, Clippy, formatting, static checks, change classification, coverage and the required CI summary. Coverage: 85.8% overall and 98.1% for formats; existing non-blocking store warning (90.5% baseline versus 87.3% measured) reviewed, baseline unchanged.

No new dependencies, version bump, test doubles, CI changes or protection bypasses.

Final local push gate: 1062 tests passed, zero failed, 3 ignored.

Merged as 93e700d. Verified tested commit is on main and issue #111 is closed. Automation-owned branch cleaned up after merge; maintainer edits were enabled while open.