Web UI: Updated tab, inline errors, mobile card fixes (#3)

Third pass on the password-gated web UI, on top of #1 and #2.

## Updated tab
New `?tab=new` tab listing only series with an unread published chapter, plus per-tab empty states for Favourites and Updated. Covered by `TestUIListNewTab`.

## Inline error feedback
htmx does not swap on a non-2xx response, so a failed favourite/chapter/delete looked like an ignored tap. Errors now render in a `.error-inline` slot on the card and clear after 5s. The chapter-edit form and delete-confirm row also close each other — only one per-card panel open at a time.

## Mobile fixes (P0)
`.chapter-form` held three children on one unwrapped flex row, pushing Save off screen: **97px of page overflow at 390px, 127px at 360px**. That broke correcting a chapter number on the primary device class.

- `.chapter-form` and `.confirm-row` wrap; hint and prompt take their own full-width row
- `.chapter-form input` uses `flex: 1 1 0; min-width: 0` — with `flex: 1` (basis auto) a number input holds its ~20ch intrinsic width and refused to shrink, which pushed Save to a third row
- `white-space: nowrap` on the confirm prompt alone reintroduced 26px of overflow; the full-width row is what actually fixes it

Verified live: `document.body.scrollWidth <= window.innerWidth` with every chapter-form and confirm-row open, at 360/390/768/1280, light and dark.

## Icons
`☆ ✎ 🗑 ▶` replaced with hand-authored inline SVG on `currentColor` — the emoji font rendered each in a different face, weight, and colour, ignoring the card's own type and colour system. `.icon.on` / `.icon.danger` / `.primary` keep driving colour. No icon font or library added.

## No-cover empty state
Series whose source site gave no `og:image` render a title-initial monogram (`Bookmark.Initial()`) instead of a blank `--surface-2` rectangle that read as a cover still loading. Shared between the card cover and the Continue-reading strip.

## Verification
- `go build ./... && go test ./...` — pass
- Live interaction run: favourite toggle round-trips, chapter save 210.5→211, All/Updated/Favourites swap, delete-confirm removes the card, no console errors

Reviewed-on: #3
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

PRODUCT.md

@@ -0,0 +1,56 @@
+# Product
+
+<!-- impeccable:product-schema 1 -->
+
+## Platform
+
+web
+
+## Users
+
+Single user (self-hosted, no accounts, no multi-user planned). Reads manga on **asurascans.com** and **demonicscans.org** primarily via Bromite on mobile, also checks/updates from a desktop browser. The web UI is the cross-device view into progress captured by the userscript while reading.
+
+## Product Purpose
+
+Tracks read-progress ("last chapter read") per manga series across two otherwise-unrelated manga sites that each have their own separate `localStorage`. A Go backend unifies bookmarks into one store; the web UI is a password-gated browser view of that store for reviewing, favouriting, correcting, or removing bookmarks, and jumping back into a series to continue reading. A background poller also refreshes each series' latest-published-chapter so the list can flag "NEW" without the user visiting the site.
+
+## Positioning
+
+Not a public reading tracker or social app — a private, self-hosted sync layer purpose-built for two specific scraped sites, with no server-side account system (single bearer token + one password-gated session).
+
+## Operating Context
+
+- Primary reading device: Bromite (mobile Chromium), where a userscript captures progress automatically.
+- Web UI is a secondary surface: checking list state, correcting a wrong chapter number, removing dead bookmarks, jumping to "continue reading."
+- Manga cover art and titles come from the source sites' `og:image`/`og:title` — real content, not placeholders.
+- List order is driven by `updated_at`, which moves only on real reading progress (not favouriting, not a newly detected chapter) — a UI constraint the redesign must not break.
+
+## Capabilities and Constraints
+
+- Two tabs: All / Favourites. Search-filter by title (client-side, `filter.js`).
+- Card actions: continue (opens source site), toggle favourite, manual chapter override, delete (with confirm).
+- "Continue reading" horizontal strip for recently-progressed series.
+- htmx-driven partial updates (card re-render on favourite/chapter/delete), no client-side framework/build step — templates are Go `html/template`, `go:embed`-ed.
+- Mobile-first is a hard functional constraint (primary device is a phone), not just a starting breakpoint.
+
+## Brand Commitments
+
+- Name: **mangaBookmark**.
+- **Dark-first is binding**: current dark-by-default / light-follows-system-preference behavior must be preserved as a design constraint, not just a starting default, because reading happens at night.
+
+## Evidence on Hand
+
+- Live templates/CSS at `backend/templates/*.html`, `backend/static/style.css` — current implemented UI, functional but not yet treated as an intentional design system.
+- No logo, screenshots, or marketing copy exist; none should be fabricated.
+
+## Product Principles
+
+- Dark-first, night-reading-optimized — never regress to a light-default or high-glare surface.
+- Mobile is the primary target; desktop is an enhancement, not the design center.
+- Progress data integrity over visual flourish: `updated_at`/list-ordering behavior is a correctness constraint the UI must respect, not decorate over.
+- No accounts, no multi-tenant chrome — the whole product is for one reader.
+- Prefer native platform affordances (system dark/light, native touch targets) over custom widgetry — this is a lean self-hosted tool, not a product to demo.
+
+## Accessibility & Inclusion
+
+Explicit personal requirement: optimized for **low-light/night reading** — minimize glare and eye strain (true dark surfaces, restrained brightness/contrast on accents, no jarring pure-white flashes), beyond generic touch-target/contrast compliance.