v0.2.3 — update notifier + Modal/TUI overhaul + Windows update

[ungaro]

Five additions, all in one release; backward-compatible — no CLI flag changes, no TxBundle shape changes, --dry-run -o json --address … flows produce identical bytes to v0.2.2.

Part 1 — Passive update notifier

• New src/version_check.rs. Runs at the top of every invocation except update/dashboard and when NEST_NO_UPDATE_CHECK=1.
• Reads ~/.cache/nest-cli/version-check.json. If cached latest_version > CARGO_PKG_VERSION (semver) → one-line stderr notice (yellow ▲ on TTY, plain ! otherwise).
• If cache is missing or older than 24 h, spawns a detached thread that fetches nestagents.io/downloads/version.json (3 s timeout) and rewrites the file. On failure (network/HTTP/parse) we still bump checked_at so we don't hammer a broken endpoint.
• nest update now writes the just-installed version into the cache so the very next invocation doesn't show a stale notice.
• Exposed pub(crate) fn cached_latest() -> Option<Version> for the planned v0.2.4 TUI banner.
• Replaces the old v0.2.1 OnceLock startup banner (which only fired on --version/--help) — single notification path, single cache file.

Part 2 — Modal picker primitive

• New src/tui/widgets/modal.rs: generic Modal<T> with centered Clear/Block/List, / filter mode, ↑↓/Enter/Esc semantics. Returns ModalAction::{None, Selected(T), Cancelled}.
• App gained pub modal: Option<(ModalKind, Modal<ModalItem>)>. Keys are trapped while a modal is open.
• ModalKind variants: VaultPicker, ChainPicker, AssetPicker, WithdrawMode, WithdrawVaultPicker, HistoryVaultPicker. ModalItem boxes large variants (Vault/Asset) to keep the enum small.

Part 3 — Deposit & Withdraw form overhaul

• DepositForm / WithdrawForm rewritten with Option<VaultDetailed> / Option<u64> (chainId) / Option<LiquidAsset> instead of typed strings; tui_input::Input for the amount/shares field (paste, cursor, MAX via Ctrl+M).
• Async balance fetcher via tokio::sync::mpsc::UnboundedChannel: wallet ERC20 balance + native balance via on-chain multicall; vault share balance via Plume RPC; instant-redeem liquidity and claimable from the actions API. Throbber while loading.
• Live deposit preview by calling EvmActionsClient::mint_build_tx under the hood (debounced 300 ms after the last keystroke) — shows the API-computed shareAmount / shareDecimals.
• Withdraw mode picker (Request / Instant / Claim); Instant/Claim are omitted from the picker when their gating fetches resolve to zero. Withdraw vault picker filtered to vaults the user has positions in (app.positions); shows "No Nest positions — deposit first" if empty.
• Inline ValidatedField + validate_amount(input, max, decimals) (Required / NotNumeric / ExceedsBalance / Other). Errors render in red below the field.
• New deps: tui-input = "0.15", throbber-widgets-tui = "0.11".

Part 4 — History page redesign (Chart + axes)

• Sparkline → ratatui::widgets::Chart + Axis per metric (APY %, TVL $K, Price $). X axis = unix timestamps formatted MMM DD (chrono); Y axis = min/mid/max ticks.
• Always-visible header bar with vault identity + latest snapshot values (7d/30d APY, TVL, Price) and the current range/offset.
• Always-visible footer hint with the new keybindings.
• New keys: v opens a vault picker (HistoryVaultPicker), [ shifts the date window backward by half the current history_days, ] shifts forward.

Part 5 — Windows nest update self-replace (rename trick)

• The v0.2.1 "Windows isn't supported, re-download manually" early-return is gone.
• install_archive is now #[cfg]-gated:
  • Unix (unchanged): .tar.gz → stage alongside dest → rename (atomic).
  • Windows (new): .zip (via zip crate, deflate only) → rename current nest.exe to nest.exe.old (you can't overwrite a running .exe but you can rename it) → write new bytes as nest.exe.
• On launch, version_check::cleanup_old_exe() sweeps any stale nest.exe.old. No-op on Unix.
• Notifier wording stays platform-agnostic ("Run `nest update`") since Windows can now self-update on x86_64. ARM64 Windows is still uncovered — the installer script will gate on that.

Verification

• cargo test — 61 passed (up from 32 before v0.2.3; new unit tests for the notifier cache/TTL/semver, Modal navigation/filter/commit, deposit/withdraw form validation, history offset).
• cargo clippy --all-targets -- -D warnings clean.
• cargo fmt -- --check clean.

Out of scope (per spec)

• ARM64 Windows release artifact — install.ps1 will surface a clear "not yet supported" error; build target deferred.
• Persistent TUI version banner — planned for v0.2.4. The cached_latest() getter is in place so v0.2.4 can read state without re-implementing parsing.
• Publishing the actual version.json to nest-agents