Embed IANA timezone database in the binary

[AevumDecessus]

What

The dashboard's schedule view renders current time using time.Now().Hour() and time.Now().Weekday() in cmd/anantha/cmd/templates.go. On minimal container base images (debian:bookworm-slim, distroless, scratch) the IANA zoneinfo files are not present, so Go's runtime falls back to UTC regardless of what the TZ environment variable says. The result is a UTC-rendered schedule grid for users in any other zone, and the notification timestamp formatter at serve.go:1006 (t.Local().Format(...)) is similarly stuck on UTC.

This PR adds a single anonymous import of time/tzdata to cmd/anantha/main.go. That embeds the IANA zone database into the binary at link time. Users still need to set TZ in their environment (e.g. TZ=America/New_York in their compose file or via environment:), but with the embed the lookup succeeds regardless of base image.

Why this approach

Three options were considered:

• Install tzdata in the Dockerfile: works, ~2.6 MB image growth, but only fixes the official Docker image. Users running anantha natively via go install github.com/anupcshan/anantha/cmd/anantha@latest still see UTC.
• Embed time/tzdata (this PR): ~400 KB binary growth, fixes both Docker and native install paths, future-proof against base-image churn (Dockerfile could later switch to scratch or distroless without breaking timezones).
• Both: trivial cost difference, but the embed alone is enough.

The embed-only approach is the minimal change that fixes the broadest set of deployment shapes.

Verification

Built locally with go build and confirmed:

• Binary size: 22.4 MB -> 22.9 MB (+403 KB / +1.8%).
• With TZ=America/New_York set, time.LoadLocation("America/New_York") succeeds and renders local hour (9 EDT) vs UTC (13). Without TZ, behavior is unchanged from main (still UTC).
• All four lint gates pass: go build, go vet, go fmt, golangci-lint (0 issues).

User-facing change

After merging, users who want local-time rendering should set TZ in their environment:

# Native:
TZ=America/New_York anantha serve ...

# Docker compose:
environment:
  - TZ=America/New_York

# Docker run:
docker run -e TZ=America/New_York ... ghcr.io/anupcshan/anantha:latest serve ...

Without TZ set, behavior is identical to today (UTC). No regression for existing deployments.