Summary

Add a zemo ls subcommand that prints topic names from <memo>/topics/ to stdout. The dump-style output (one per line, alphabetical, no .md extension) is feed-back compatible with zemo <topic> and intended to integrate with terminal-side search (e.g. WezTerm QuickSearch) instead of an embedded picker.

Related issue

Closes #3

Changes

• New Command.ls variant in cli.zig; routed from parseArgs and dispatched in run.
• New doLs (env → path resolution) and listTopics (path-based, testable) helpers.
• <memo>/topics/ missing → exit 0 with no output (treated as empty memo).
• Output filters to *.md files only; subdirectories and other extensions are skipped; trailing .md is stripped from each line.
• paths.memoDir: convert relative ZEMO_DIR to absolute via std.process.currentPathAlloc. Pre-existing latent bug — Io.Dir.*Absolute calls in openScratch / openTopic / doSync would assert on a relative ZEMO_DIR. Fixed centrally so all commands benefit.
• README: added zemo ls to Features and Usage sections.
• HELP_TEXT: added zemo ls line.

Testing

• zig build test passes locally
• Manually verified the affected command(s) (zig build run -- ls against ~/memo)
• Smoke tested relative ZEMO_DIR (ZEMO_DIR=./relmemo zemo ls) — no panic, correct output
• Cross-build check (if touching platform-specific code): zig build -Dtarget=x86_64-windows / -Dtarget=x86_64-macos

New tests added:

• parseArgs: ls subcommand — parser-level
• listTopics: alphabetical order, only .md files — integration test using std.testing.tmpDir and Io.Writer.Allocating to capture output
• absolutePath: keeps absolute paths / absolutePath: resolves relative paths from cwd — unit tests in paths.zig for the new normalization helper

Notes for reviewers

• listTopics was extracted from doLs to keep the testable surface path-based (mirrors the resolveMemoDir / memoDir split in paths.zig).
• The paths.memoDir signature gained an io parameter so it can read cwd; all existing call sites (openScratch / openTopic / doSync) updated accordingly.