docs: remove README Important security admonition (#207)

[miso-develop]

Closes #207

Scope

• remove the opening [!IMPORTANT] public-repository warning block from README.md
• remove the equivalent opening warning block from README.ja.md
• preserve ordinary SECURITY.md references in both READMEs
• leave AGENTS.md unchanged because current main already explicitly requires agents to read/follow SECURITY.md
• no product/runtime/security-policy behavior changes

Verification

HEAD: 89aa0fa45b3d5ec643830bd2c703d4cc582c6ec4

• README diff is exactly two files: README.md and README.ja.md
• each README deletes only the three-line opening admonition block
• neither README contains [!IMPORTANT] or an empty warning blockquote
• ordinary SECURITY.md references remain in both READMEs
• AGENTS.md remains unchanged and still contains multiple explicit SECURITY.md requirements
• EN/JA heading hierarchy remains structurally equivalent
• current main is unchanged from claim baseline 40f7061eb89dcc676599d7f74f1b45037e589ea2; branch is behind 0
• open PR fix(web): prevent USB Serial teardown reset (#204) #206 is Web Serial lifecycle work and does not overlap this README surface
• Security #935: SUCCESS
• Foundation #932: SUCCESS

No Product, Protocol, Vault, Device, Web runtime, release-policy, or SECURITY.md behavior changes.

[miso-develop]

Implementation for #207 is complete at exact HEAD 89aa0fa45b3d5ec643830bd2c703d4cc582c6ec4.

Verification:

• README.md: opening [!IMPORTANT] block removed; ordinary SECURITY.md references preserved.
• README.ja.md: equivalent opening admonition removed; ordinary SECURITY.md references preserved.
• no empty admonition/blockquote remains.
• EN/JA heading hierarchy remains equivalent.
• AGENTS.md was intentionally not modified and still explicitly requires/reference SECURITY.md in multiple places.
• effective diff is exactly the two README files, three deleted lines each.
• current main remains 40f7061eb89dcc676599d7f74f1b45037e589ea2; branch behind 0.
• open PR fix(web): prevent USB Serial teardown reset (#204) #206 is Web-only and non-overlapping.
• Security #935: SUCCESS.
• Foundation #932: SUCCESS.

No security-policy, runtime, Protocol, Vault, release, Device, or Web behavior change.

[miso-develop]

HANDOFF
FROM: implementation
TO: review
DOMAIN: infra
ISSUE: #207
PR: #209
HEAD: 89aa0fa
STATE: READY_FOR_REVIEW

[miso-develop]

Review disposition: READY_FOR_INTEGRATION

Reviewed exact PR head 89aa0fa45b3d5ec643830bd2c703d4cc582c6ec4 against Issue #207 and the #192 product-facing README baseline.

No blocking finding identified.

Scope verification:

• Effective diff is exactly two files:
  • README.md
  • README.ja.md
• Each README removes exactly the opening three-line GitHub Markdown Important admonition block.
• No empty blockquote/admonition shell remains.
• No unrelated README section was rewritten.
• AGENTS.md is unchanged, as required.

Security-policy continuity:

• The prominent README warning is removed without weakening the authoritative repository policy.
• README.md still references SECURITY.md in:
  • the authoritative security-contract section;
  • the Security Policy documentation entry;
  • the development/contribution reminder.
• README.ja.md preserves the equivalent three SECURITY.md references.
• AGENTS.md independently continues to require SECURITY.md in multiple normative places, including:
  • credential-like value handling;
  • bootstrap/read requirements;
  • security-sensitive change review;
  • completion/security gates.
• SECURITY.md itself is untouched.
• No secret-handling requirement, Product/Protocol/Vault/crypto/Device/Web runtime/release-policy behavior is changed.

EN/JA parity:

• Both languages remove the corresponding opening admonition.
• Heading hierarchy and product-first README structure remain unchanged/equivalent.

Exact-head evidence:

• Security #935: SUCCESS, including repository security scan and existing security-contract checks.
• Foundation #932: SUCCESS, including Web, Windows Chrome, firmware regression/security contracts, isolated ESP-IDF build/package validation, and dependency-lock verification.

Staleness/collision:

• Handoff HEAD matches current PR HEAD.
• PR is open, non-draft, and mergeable.
• Current main remains exact PR base 40f7061eb89dcc676599d7f74f1b45037e589ea2.
• Compare is 2 commits ahead / 0 behind.
• Open PR #206 is Web Serial lifecycle work and does not touch README/AGENTS.
• Open PR #210 is Web presentation/layout work and does not touch README/AGENTS.
• No ownership or file collision exists.

No additional Security review or Human Gate is required for this documentation-only change.

[miso-develop]

HANDOFF
FROM: review
TO: integration
ISSUE: #207
PR: #209
HEAD: 89aa0fa
STATE: READY_FOR_INTEGRATION

[miso-develop]

READY_TO_MERGE

HEAD: 89aa0fa45b3d5ec643830bd2c703d4cc582c6ec4
Current main: 40f7061eb89dcc676599d7f74f1b45037e589ea2

Integration reconstruction:

• exact PR head matches Review handoff
• PR is open, non-draft, mergeable
• Review disposition: READY_FOR_INTEGRATION; no blocking finding
• Security #935: SUCCESS
• Foundation #932: SUCCESS
• no unresolved review threads
• PR base equals current main
• fix(web): prevent USB Serial teardown reset (#204) #206 is Web Serial lifecycle work and non-overlapping
• style(web): add space before passphrase divider (#208) #210 is Web presentation/layout work and non-overlapping
• no Human Gate required
• no additional Security review required

STATE: READY_TO_MERGE

[miso-develop]

INTEGRATED

PR: #209
Pre-merge HEAD: 89aa0fa45b3d5ec643830bd2c703d4cc582c6ec4
Squash merge commit / current main: 3432bcda8af5a4c4a09bafadebec9ae1484f9460

Integration evidence:

• Review: READY_FOR_INTEGRATION at exact head
• Security #935: SUCCESS
• Foundation #932: SUCCESS
• no unresolved review threads
• no Human Gate required
• no additional Security review required
• Issue [Chore][Repository] Remove README Important security admonition #207 auto-closed as completed

STATE: INTEGRATED