Support isolated Sage data roots

[Rigidity]

Summary

• add a shared SAGE_ROOT override for desktop, CLI, and RPC clients
• route wallet, app database, app storage, and Windows webview profile data through the selected root
• document multi-instance usage and the need for distinct RPC ports

Test plan

• cargo fmt --all -- --files-with-diff --check
• cargo clippy --workspace --all-features --all-targets
• cargo test -p sage-config -p sage-apps -p sage-client -p sage-cli -p sage-tauri

---

Note

Medium Risk
Changes where wallets, TLS material, app DB, and webview storage live; misconfigured or shared roots could mix instances, though default behavior is unchanged when SAGE_ROOT is unset.

Overview
Adds a shared SAGE_ROOT override so desktop, sage rpc, and the RPC client can use the same on-disk root instead of only the default OS data directory (com.rigidnetwork.sage).

sage-config centralizes resolution in sage_root() / sage_root_override(); CLI and client drop direct dirs usage and read config/certs from that root. The Tauri setup uses the override when set, otherwise keeps Tauri’s app data dir, and passes that path into Sage and the apps DB.

sage-apps stores the root on AppsHostState and routes bridge grants, storage rotation, Windows WebView2 profile dirs, and abandoned-profile cleanup under it (profiles live under {root}/profiles/...). README documents running multiple dev instances and using distinct RPC ports per root’s config.toml.

^{Reviewed by Cursor Bugbot for commit c6f7d11. Bugbot is set up for automated code reviews on this repo. Configure here.}