Add Copilot skill architecture with 10 skills, 2 agents, and shared infra

Introduce .github/skills/ with solve, prove, optimize, simplify,
encode, explain, benchmark, memory-safety, static-analysis, and
deeptest skills. Each skill follows a SKILL.md + scripts/ pattern
with Python scripts backed by a shared SQLite logging library
(z3db.py). Two orchestrator agents (z3-solver, z3-verifier) route
requests to the appropriate skills.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/skills/simplify/SKILL.md

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+---
+name: simplify
+description: Reduce formula complexity using Z3 tactic chains. Supports configurable tactic pipelines for boolean, arithmetic, and bitvector simplification.
+---
+
+Given a formula, apply a sequence of Z3 tactics to produce an equivalent but simpler form. This is useful for understanding what Z3 sees after preprocessing, debugging tactic selection, and reducing formula size before solving.
+
+# Step 1: Choose tactics
+
+Z3 provides dozens of tactics. Common ones:
+
+| Tactic | What it does |
+|--------|-------------|
+| simplify | constant folding, algebraic identities |
+| propagate-values | substitute known equalities |
+| ctx-simplify | context-dependent simplification |
+| elim-uncnstr | remove unconstrained variables |
+| solve-eqs | Gaussian elimination |
+| bit-blast | reduce bitvectors to booleans |
+| tseitin-cnf | convert to CNF |
+| aig | and-inverter graph reduction |
+
+# Step 2: Run simplification
+
+```bash
+python3 scripts/simplify.py --formula "(assert (and (> x 0) (> x 0)))" --vars "x:Int"
+python3 scripts/simplify.py --file formula.smt2 --tactics "simplify,propagate-values,ctx-simplify"
+python3 scripts/simplify.py --file formula.smt2 --debug
+```
+
+Without `--tactics`, the script applies the default chain: `simplify`, `propagate-values`, `ctx-simplify`.
+
+# Step 3: Interpret the output
+
+The script prints the simplified formula in SMT-LIB2 syntax. Subgoals are printed as separate `(assert ...)` blocks.
+
+# Parameters
+
+| Parameter | Type | Required | Default | Description |
+|-----------|------|----------|---------|-------------|
+| formula | string | no | | SMT-LIB2 formula to simplify |
+| vars | string | no | | variable declarations as "name:sort" pairs |
+| file | path | no | | path to .smt2 file |
+| tactics | string | no | simplify,propagate-values,ctx-simplify | comma-separated tactic names |
+| timeout | int | no | 30 | seconds |
+| z3 | path | no | auto | path to z3 binary |
+| debug | flag | no | off | verbose tracing |
+| db | path | no | .z3-agent/z3agent.db | logging database |

.github/skills/simplify/scripts/simplify.py

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+#!/usr/bin/env python3
+"""
+simplify.py: apply Z3 tactics to simplify an SMT-LIB2 formula.
+
+Usage:
+    python simplify.py --formula "(assert (and (> x 0) (> x 0)))" --vars "x:Int"
+    python simplify.py --file formula.smt2 --tactics "simplify,solve-eqs"
+"""
+
+import argparse
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent.parent / "shared"))
+from z3db import Z3DB, run_z3, setup_logging
+
+
+DEFAULT_TACTICS = "simplify,propagate-values,ctx-simplify"
+
+
+def build_tactic_formula(base_formula: str, tactics: str) -> str:
+    tactic_list = [t.strip() for t in tactics.split(",")]
+    if len(tactic_list) == 1:
+        tactic_expr = f"(then {tactic_list[0]} skip)"
+    else:
+        tactic_expr = "(then " + " ".join(tactic_list) + ")"
+    return base_formula + f"\n(apply {tactic_expr})\n"
+
+
+def build_formula_from_parts(formula_str: str, vars_str: str) -> str:
+    lines = []
+    if vars_str:
+        for v in vars_str.split(","):
+            v = v.strip()
+            name, sort = v.split(":")
+            lines.append(f"(declare-const {name.strip()} {sort.strip()})")
+    lines.append(formula_str)
+    return "\n".join(lines)
+
+
+def main():
+    parser = argparse.ArgumentParser(prog="simplify")
+    parser.add_argument("--formula")
+    parser.add_argument("--vars")
+    parser.add_argument("--file")
+    parser.add_argument("--tactics", default=DEFAULT_TACTICS)
+    parser.add_argument("--timeout", type=int, default=30)
+    parser.add_argument("--z3", default=None)
+    parser.add_argument("--db", default=None)
+    parser.add_argument("--debug", action="store_true")
+    args = parser.parse_args()
+
+    setup_logging(args.debug)
+
+    if args.file:
+        base = Path(args.file).read_text()
+    elif args.formula:
+        base = build_formula_from_parts(args.formula, args.vars or "")
+    else:
+        parser.error("provide --formula or --file")
+        return
+
+    formula = build_tactic_formula(base, args.tactics)
+
+    db = Z3DB(args.db)
+    run_id = db.start_run("simplify", formula)
+
+    result = run_z3(formula, z3_bin=args.z3, timeout=args.timeout, debug=args.debug)
+
+    status = "success" if result["exit_code"] == 0 else "error"
+    db.log_formula(run_id, formula, status)
+    db.finish_run(run_id, status, result["duration_ms"], result["exit_code"])
+
+    print(result["stdout"])
+    if result["stderr"] and result["exit_code"] != 0:
+        print(result["stderr"], file=sys.stderr)
+
+    db.close()
+    sys.exit(0 if result["exit_code"] == 0 else 1)
+
+
+if __name__ == "__main__":
+    main()