refactor(zig): migrate codebase from 0.15.2 to 0.16.0

[pocky]

Summary

• Migrate the entire ztick codebase from Zig 0.15.2 to 0.16.0, adopting breaking API changes across I/O namespaces, threading primitives, the build system, and the main entry point signature
• Bump zig-o11y/opentelemetry-sdk to v0.2.0 and sam701/zig-cli to the main branch (v0.11.0), both required for 0.16 compatibility
• Fix 9 of 11 functional test failures introduced by the migration, including graceful HTTP shutdown coordination and a memory leak in the test helper
• Restructure CLAUDE.md to delegate queryable rules (architecture, pitfalls, tests, review) to a new ZPM knowledge base, replacing inline markdown lists

Changes

Build system & CI

• build.zig: Switch to root_module.link_libc, root_module.linkSystemLibrary with options struct, pass b.graph.io to handle.access, drop explicit target/optimize forwarding to dependencies (0.16 propagates them automatically)
• build.zig.zon: Bump minimum_zig_version to 0.16.0; update OTel hash to v0.2.0 and zig-cli hash to main branch (v0.11.0)
• Makefile: Add --test-timeout 30s to integration test invocations
• .github/workflows/ci.yaml: Update all four jobs (lint, test, sanitize, build) from Zig 0.15.2 → 0.16.0
• .github/workflows/release.yaml: Bump ZIG_VERSION env var to 0.16.0

Application layer

• src/application/scheduler.zig: Migrate std.time / threading primitives to 0.16 equivalents; thread io: std.Io through scheduler context
• src/application/execution_client.zig: Update I/O and process APIs
• src/application/job_storage.zig: Namespace and API fixes
• src/application/query_handler.zig: I/O namespace migration

Infrastructure — I/O and concurrency

• src/infrastructure/clock.zig: Replace std.time.Instant with std.Io.Clock.Timestamp; cache io on struct to preserve allocation-free tick semantics
• src/infrastructure/channel.zig: Replace std.Thread.Mutex/Condition with std.Io.Mutex/Condition; fix timedWait signature
• src/infrastructure/tcp_server.zig: Migrate std.net → std.Io.net, update stream reader/writer pattern, fix graceful shutdown signaling
• src/infrastructure/http.zig: Migrate std.http.Server to 0.16 reader/writer interface; wire HTTP shutdown to signal handler; update Reader/Writer types
• src/infrastructure/http/json.zig: Namespace update
• src/infrastructure/telemetry.zig: Adopt OTel SDK v0.2.0 init signature; fix io_rng lifetime for telemetry setup
• src/infrastructure/auth.zig: Update socket/poll APIs (remove std.posix, use std.os.linux syscalls)
• src/infrastructure/tls_context.zig: Fix @cImport and pointer-cast idioms for 0.16

Infrastructure — persistence

• src/infrastructure/persistence/backend.zig: Migrate I/O file APIs
• src/infrastructure/persistence/background.zig: Thread io parameter; update threading primitives
• src/infrastructure/persistence/logfile.zig: Namespace update

Infrastructure — protocol & runners

• src/infrastructure/protocol/parser.zig: Namespace update
• src/infrastructure/redis/resp.zig: Migrate std.io.fixedBufferStream → std.Io.Reader.fixed/std.Io.Writer.fixed
• src/infrastructure/runner.zig, runner/amqp.zig, runner/awf.zig, runner/direct.zig, runner/http.zig, runner/redis.zig, runner/shell.zig, runner/subprocess.zig: Update I/O, process spawn, and stream APIs throughout

Entry point & interfaces

• src/main.zig: Adopt Juicy Main (pub fn main(init: std.process.Init) !void); source GPA, args, and io from init; replace @Type(.enum_literal) with @EnumLiteral; update signal handler type to fn(std.os.linux.SIG) callconv(.c) void; thread io through all subsystems
• src/interfaces/cli.zig: Route init.minimal.args via Args.Iterator.initAllocator; remove std.process.argsAlloc/argsFree
• src/interfaces/config.zig: Update TOML parsing I/O
• src/interfaces/dump.zig: Migrate file I/O APIs

Tests

• src/functional_tests.zig: Overhaul 1874-line test file — fix TestServer.start/stop to use std.Io child process APIs, add atomic shutdown signaling, fix TestServer memory leak (free config_path via allocator.free directly), fix telemetry io_rng lifetime, add defer-based cleanup

Documentation & project metadata

• CHANGELOG.md: Add F024 migration entry under [Unreleased]
• CLAUDE.md: Replace inline rule lists with ZPM query references; add ZPM project memory section with segment definitions and query patterns
• CONTRIBUTING.md, README.md: Bump Zig prerequisite to 0.16.0+
• docs/ADR/0002-zig-language-choice.md, 0003-openssl-tls-dependency.md, 0004-opentelemetry-sdk-dependency.md, 0005-amqp-runner-design.md, 0006-redis-runner-design.md: Update version references to 0.16.0
• docs/development/building.md, docs/tutorials/getting-started.md: Update Zig version prerequisites
• .gitignore: Add zig-pkg/, *.o, and AWF/web project artifact patterns

ZPM knowledge base

• .zpm/kb/default/knowledge.pl, journal.wal: Base schema for task graphs, components, ADRs, and project memory
• .zpm/kb/feedback/knowledge.pl, journal.wal: 40+ queryable architecture, pitfall, test, and review rules migrated from CLAUDE.md
• .zpm/kb/migration_zig016/knowledge.pl, journal.wal: Migration scope, breaking changes, verified APIs, and corrections recorded during F024
• .zpm/kb/pr_feature_f024_zig_0152_0160_migration/knowledge.pl, journal.wal: PR task completion tracking
• .zpm/mounts.json: Mount configuration for all four segments
• .zpm/kb/before_commit_20260427_160139.pl: Deleted obsolete snapshot file

Test plan

• make build compiles with Zig 0.16.0 (no deprecation errors or API failures)
• zig build test-all passes all unit tests across all layers (domain, application, infrastructure, interfaces)
• zig build test-functional passes with no memory leaks reported by DebugAllocator
• CI pipeline (lint → test → sanitize → build) runs green with mlugg/setup-zig@v2 installing version 0.16.0

Closes #48

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