fix repl-block, check-tangle, commands: READMEs, exit codes, path resolution

repl-block:
- Listing mode exits 0, not 1 (listing is not an error)
- Dead lines parameter removed from find_by_function
- Block listing goes to stderr (not stdout) so piped use works
- Added README.org

check-tangle:
- Fixed tangle tool resolution: prefer local projects/tangle-tool/tangle
- Fixed path resolution for relative and absolute tangle paths
- Removed 2>/dev/null suppression so tangle errors are visible
- Added README.org

Commands:
- Rewrote all three .opencode/commands/*.md with proper prompts

.opencode/commands/check-tangle.md

@@ -3,6 +3,13 @@ description: Tangle an org file and compile the result
 ---
 
 Tangle an .org file to .lisp then compile with SBCL. Reports the first
-compile error. Exit 0 = clean, exit 1 = compilation error.
+compile error with line numbers. Exit 0 = clean compile, exit 1 = error.
+
+Prepares code for commit by ensuring the tangled .lisp file is syntactically
+valid. Catches missing symbols, undefined functions, and type errors before
+they reach the running daemon.
 
 Usage: /check-tangle <file.org>
+
+Example:
+  /check-tangle projects/passepartout/org/channel-tui-main.org