Add project issues for lush (Lua + shell) features

Defines syntax decisions and implementation plan across 7 issues:
- backtick command execution returning {code, stdout, stderr}
- ${expr} interpolation in backticks
- $SIGIL env var read/write
- argv parsing, piping, and redirection (future)

issues/02-backtick-lexing-parsing.md

@@ -0,0 +1,23 @@
+# 02 — Complete backtick command lexing and parsing
+
+**Status:** open
+**Blocked by:** #01
+**Blocks:** #03
+
+Backtick lexing is partially implemented:
+- `llex.c`: TK_COMMAND token lexed via `read_string()` on backtick
+- `llex.h`: TK_COMMAND enum added
+- `lparser.c`: TK_COMMAND handled in `simpleexp()` (as string) and `suffixedexp()` (as func args)
+
+## Remaining work
+
+- Verify the lexer handles edge cases (escaped backticks, newlines, nested quotes)
+- Parser must emit code that produces a result table (`{code, stdout, stderr}`) at runtime, not just a string literal
+- May need a new opcode (e.g. `OP_COMMAND`) or compile as a call to a built-in execution function
+- Add string interpolation inside backticks if decided in #01
+
+## Files touched
+
+- `llex.c` / `llex.h`
+- `lparser.c`
+- Possibly `lopcodes.h` / `lopcodes.c` if adding a new opcode