Epic: make graith runtime policy config-driven

## Goal

Move user-facing runtime policy, product defaults, and tunable operational limits out of scattered Go/Swift literals and into graith's effective TOML configuration.

This tracks the hard-coded-value audit performed on 2026-07-16. Child issues split the work by subsystem so changes can ship independently.

## Principle

A value belongs in configuration when operators may reasonably need to tune it, clients must agree on it, or it changes product behaviour. The embedded default configuration should remain the single source of defaults, and `gr config show` should display the complete effective result.

## Deliberate exclusions

Keep true implementation invariants in code, including:

- protocol channels, frame header/layout, protocol and state schema versions
- cryptographic sizes, signature/TLS requirements, and file permission modes
- terminal encoding/control-sequence constants
- minimum supported backend/kernel versions
- small defensive bounds whose configurability would weaken safety

Each child issue must classify its literals before exposing knobs; the goal is config-driven policy, not indiscriminate configurability.

## Configuration and agent integration

- [x] #1237
- [x] #1234
- [x] #1235
- [x] #1233
- [x] #1232
- [x] #1236

## Connectivity and lifecycle

- [x] #1242
- [ ] #1238
- [x] #1241
- [x] #1243
- [x] #1239

## Automation, monitoring, and storage

- [x] #1240
- [x] #1248
- [x] #1244
- [x] #1245
- [x] #1246
- [x] #1247
- [x] #1249

## Limits, approvals, updates, and clients

- [x] #1252
- [x] #1250
- [x] #1251
- [x] #1253
- [x] #1254
- [x] #1255

Start with the completed and open child issues listed under Configuration and agent integration, Connectivity and lifecycle, Automation, monitoring, and storage, and Limits, approvals, updates, and clients. Review the effective TOML configuration, embedded default configuration, and `gr config show` behavior before classifying hard-coded values. Done means the appropriate child work is completed while implementation invariants remain in code and the effective configuration shows the complete result.

Written by the indexing model from the issue text.