Vim navigation refactor: declarative "navigable elements" (epic)

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Stub. Plan in detail when we get to it.

Problem

Vim navigation is per-page. Every view (info, ideas, economics, news cards, sketch metrics, AI trading panels, financials rows, SEC filings rows, sector items …) has its own j / k / h / l / Enter handler hand-coded in terminal.js. Each handler knows about the specific DOM structure it operates on. Side-effects:

• New pages start broken. The crypto / forex / index / ETF stubs from Security types — foundation (routes + dispatch + legacy redirect) #98 ship with no tab navigation — pressing j/k does nothing because none of the existing per-page handlers match. The user has to mouse to switch tabs until each type's vim handler is bolted on.
• Adding a new tab or section means editing both the page's render code AND the corresponding handler block in terminal.js. Easy to forget; easy to drift.
• Cross-page nav semantics differ (e.g. j in news cards advances cards; j in AI tab enters content focus; j in financials tab enters rows). Inconsistent friction.

Insert mode (Esc) and search (s) work fine — they're global. Navigation should be too.

What we want

A first-class navigable element concept. Any element in any template can opt in by declaring itself navigable (e.g. data-vim="item" or a CSS class). The shared vim core handles:

• j / k move focus to the next / previous navigable element in DOM order.
• h / l move across a sibling group (tabs row, sub-tabs row, column grids) — defined by a navigable element being a "group".
• Enter triggers the element's primary action (defined by data-vim-action="…" or by being a link / button).
• Selected state via a single shared .vim-selected CSS class — no more per-page selection classes.
• Scoping: a "focused container" (the current view's content area) is the default search root. Nested navigable groups can be entered/exited with j/k boundaries.

Page authors should add nav by adding attributes to the template, not by writing a JS handler.

Why this matters beyond consistency

This is a prerequisite for #94 (per-paragraph p → pop chart) and the broader "pin a paragraph + chart to an idea" goal. Once paragraphs are first-class navigable elements, pinning, sharing, and attachment all become annotations on the same primitive.

It also lets the new type-specific pages from #97 (crypto / forex / index / etf) ship navigation for free instead of duplicating the info-tab handlers four times.

Out of scope (for the eventual plan)

• Not a complete rewrite of terminal.js — keep the global key dispatcher and the search bar / insert-mode plumbing as-is.
• Not a swap to a framework. Vanilla JS, in-place refactor.

Pre-work / context

• Current per-page handlers live in internal/server/static/terminal.js (see vimHandlers.{ideas, economics, watchlist, graph, news, info} and info._focus = main|sub|content).
• Recent work on the AI tab (feat: multi-agent trading analysis pipeline (phase 1) #39, fix(info): vim flow into Run Deep Analysis button #92) already uses a data-trading-vim attribute pattern — a small precedent for declarative nav.
• The financials tab (_finGetRows), SEC tab (_secGetRows), trading-panels (_tradingVimHandler) all expose the same shape (rows + selected idx + enter handler) through window.* globals — strong signal these should unify.

When this gets picked up, plan it as its own epic with discrete migration issues per existing view.